diff options
Diffstat (limited to 'fs/file.c')
| -rw-r--r-- | fs/file.c | 1336 |
1 files changed, 1336 insertions, 0 deletions
diff --git a/fs/file.c b/fs/file.c new file mode 100644 index 0000000000..3e4a4dfa38 --- /dev/null +++ b/fs/file.c @@ -0,0 +1,1336 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * linux/fs/file.c + * + * Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes + * + * Manage the dynamic fd arrays in the process files_struct. + */ + +#include <linux/syscalls.h> +#include <linux/export.h> +#include <linux/fs.h> +#include <linux/kernel.h> +#include <linux/mm.h> +#include <linux/sched/signal.h> +#include <linux/slab.h> +#include <linux/file.h> +#include <linux/fdtable.h> +#include <linux/bitops.h> +#include <linux/spinlock.h> +#include <linux/rcupdate.h> +#include <linux/close_range.h> +#include <net/sock.h> + +#include "internal.h" + +unsigned int sysctl_nr_open __read_mostly = 1024*1024; +unsigned int sysctl_nr_open_min = BITS_PER_LONG; +/* our min() is unusable in constant expressions ;-/ */ +#define __const_min(x, y) ((x) < (y) ? (x) : (y)) +unsigned int sysctl_nr_open_max = + __const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG; + +static void __free_fdtable(struct fdtable *fdt) +{ + kvfree(fdt->fd); + kvfree(fdt->open_fds); + kfree(fdt); +} + +static void free_fdtable_rcu(struct rcu_head *rcu) +{ + __free_fdtable(container_of(rcu, struct fdtable, rcu)); +} + +#define BITBIT_NR(nr) BITS_TO_LONGS(BITS_TO_LONGS(nr)) +#define BITBIT_SIZE(nr) (BITBIT_NR(nr) * sizeof(long)) + +/* + * Copy 'count' fd bits from the old table to the new table and clear the extra + * space if any. This does not copy the file pointers. Called with the files + * spinlock held for write. + */ +static void copy_fd_bitmaps(struct fdtable *nfdt, struct fdtable *ofdt, + unsigned int count) +{ + unsigned int cpy, set; + + cpy = count / BITS_PER_BYTE; + set = (nfdt->max_fds - count) / BITS_PER_BYTE; + memcpy(nfdt->open_fds, ofdt->open_fds, cpy); + memset((char *)nfdt->open_fds + cpy, 0, set); + memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy); + memset((char *)nfdt->close_on_exec + cpy, 0, set); + + cpy = BITBIT_SIZE(count); + set = BITBIT_SIZE(nfdt->max_fds) - cpy; + memcpy(nfdt->full_fds_bits, ofdt->full_fds_bits, cpy); + memset((char *)nfdt->full_fds_bits + cpy, 0, set); +} + +/* + * Copy all file descriptors from the old table to the new, expanded table and + * clear the extra space. Called with the files spinlock held for write. + */ +static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt) +{ + size_t cpy, set; + + BUG_ON(nfdt->max_fds < ofdt->max_fds); + + cpy = ofdt->max_fds * sizeof(struct file *); + set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *); + memcpy(nfdt->fd, ofdt->fd, cpy); + memset((char *)nfdt->fd + cpy, 0, set); + + copy_fd_bitmaps(nfdt, ofdt, ofdt->max_fds); +} + +/* + * Note how the fdtable bitmap allocations very much have to be a multiple of + * BITS_PER_LONG. This is not only because we walk those things in chunks of + * 'unsigned long' in some places, but simply because that is how the Linux + * kernel bitmaps are defined to work: they are not "bits in an array of bytes", + * they are very much "bits in an array of unsigned long". + * + * The ALIGN(nr, BITS_PER_LONG) here is for clarity: since we just multiplied + * by that "1024/sizeof(ptr)" before, we already know there are sufficient + * clear low bits. Clang seems to realize that, gcc ends up being confused. + * + * On a 128-bit machine, the ALIGN() would actually matter. In the meantime, + * let's consider it documentation (and maybe a test-case for gcc to improve + * its code generation ;) + */ +static struct fdtable * alloc_fdtable(unsigned int nr) +{ + struct fdtable *fdt; + void *data; + + /* + * Figure out how many fds we actually want to support in this fdtable. + * Allocation steps are keyed to the size of the fdarray, since it + * grows far faster than any of the other dynamic data. We try to fit + * the fdarray into comfortable page-tuned chunks: starting at 1024B + * and growing in powers of two from there on. + */ + nr /= (1024 / sizeof(struct file *)); + nr = roundup_pow_of_two(nr + 1); + nr *= (1024 / sizeof(struct file *)); + nr = ALIGN(nr, BITS_PER_LONG); + /* + * Note that this can drive nr *below* what we had passed if sysctl_nr_open + * had been set lower between the check in expand_files() and here. Deal + * with that in caller, it's cheaper that way. + * + * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise + * bitmaps handling below becomes unpleasant, to put it mildly... + */ + if (unlikely(nr > sysctl_nr_open)) + nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1; + + fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL_ACCOUNT); + if (!fdt) + goto out; + fdt->max_fds = nr; + data = kvmalloc_array(nr, sizeof(struct file *), GFP_KERNEL_ACCOUNT); + if (!data) + goto out_fdt; + fdt->fd = data; + + data = kvmalloc(max_t(size_t, + 2 * nr / BITS_PER_BYTE + BITBIT_SIZE(nr), L1_CACHE_BYTES), + GFP_KERNEL_ACCOUNT); + if (!data) + goto out_arr; + fdt->open_fds = data; + data += nr / BITS_PER_BYTE; + fdt->close_on_exec = data; + data += nr / BITS_PER_BYTE; + fdt->full_fds_bits = data; + + return fdt; + +out_arr: + kvfree(fdt->fd); +out_fdt: + kfree(fdt); +out: + return NULL; +} + +/* + * Expand the file descriptor table. + * This function will allocate a new fdtable and both fd array and fdset, of + * the given size. + * Return <0 error code on error; 1 on successful completion. + * The files->file_lock should be held on entry, and will be held on exit. + */ +static int expand_fdtable(struct files_struct *files, unsigned int nr) + __releases(files->file_lock) + __acquires(files->file_lock) +{ + struct fdtable *new_fdt, *cur_fdt; + + spin_unlock(&files->file_lock); + new_fdt = alloc_fdtable(nr); + + /* make sure all fd_install() have seen resize_in_progress + * or have finished their rcu_read_lock_sched() section. + */ + if (atomic_read(&files->count) > 1) + synchronize_rcu(); + + spin_lock(&files->file_lock); + if (!new_fdt) + return -ENOMEM; + /* + * extremely unlikely race - sysctl_nr_open decreased between the check in + * caller and alloc_fdtable(). Cheaper to catch it here... + */ + if (unlikely(new_fdt->max_fds <= nr)) { + __free_fdtable(new_fdt); + return -EMFILE; + } + cur_fdt = files_fdtable(files); + BUG_ON(nr < cur_fdt->max_fds); + copy_fdtable(new_fdt, cur_fdt); + rcu_assign_pointer(files->fdt, new_fdt); + if (cur_fdt != &files->fdtab) + call_rcu(&cur_fdt->rcu, free_fdtable_rcu); + /* coupled with smp_rmb() in fd_install() */ + smp_wmb(); + return 1; +} + +/* + * Expand files. + * This function will expand the file structures, if the requested size exceeds + * the current capacity and there is room for expansion. + * Return <0 error code on error; 0 when nothing done; 1 when files were + * expanded and execution may have blocked. + * The files->file_lock should be held on entry, and will be held on exit. + */ +static int expand_files(struct files_struct *files, unsigned int nr) + __releases(files->file_lock) + __acquires(files->file_lock) +{ + struct fdtable *fdt; + int expanded = 0; + +repeat: + fdt = files_fdtable(files); + + /* Do we need to expand? */ + if (nr < fdt->max_fds) + return expanded; + + /* Can we expand? */ + if (nr >= sysctl_nr_open) + return -EMFILE; + + if (unlikely(files->resize_in_progress)) { + spin_unlock(&files->file_lock); + expanded = 1; + wait_event(files->resize_wait, !files->resize_in_progress); + spin_lock(&files->file_lock); + goto repeat; + } + + /* All good, so we try */ + files->resize_in_progress = true; + expanded = expand_fdtable(files, nr); + files->resize_in_progress = false; + + wake_up_all(&files->resize_wait); + return expanded; +} + +static inline void __set_close_on_exec(unsigned int fd, struct fdtable *fdt) +{ + __set_bit(fd, fdt->close_on_exec); +} + +static inline void __clear_close_on_exec(unsigned int fd, struct fdtable *fdt) +{ + if (test_bit(fd, fdt->close_on_exec)) + __clear_bit(fd, fdt->close_on_exec); +} + +static inline void __set_open_fd(unsigned int fd, struct fdtable *fdt) +{ + __set_bit(fd, fdt->open_fds); + fd /= BITS_PER_LONG; + if (!~fdt->open_fds[fd]) + __set_bit(fd, fdt->full_fds_bits); +} + +static inline void __clear_open_fd(unsigned int fd, struct fdtable *fdt) +{ + __clear_bit(fd, fdt->open_fds); + __clear_bit(fd / BITS_PER_LONG, fdt->full_fds_bits); +} + +static unsigned int count_open_files(struct fdtable *fdt) +{ + unsigned int size = fdt->max_fds; + unsigned int i; + + /* Find the last open fd */ + for (i = size / BITS_PER_LONG; i > 0; ) { + if (fdt->open_fds[--i]) + break; + } + i = (i + 1) * BITS_PER_LONG; + return i; +} + +/* + * Note that a sane fdtable size always has to be a multiple of + * BITS_PER_LONG, since we have bitmaps that are sized by this. + * + * 'max_fds' will normally already be properly aligned, but it + * turns out that in the close_range() -> __close_range() -> + * unshare_fd() -> dup_fd() -> sane_fdtable_size() we can end + * up having a 'max_fds' value that isn't already aligned. + * + * Rather than make close_range() have to worry about this, + * just make that BITS_PER_LONG alignment be part of a sane + * fdtable size. Becuase that's really what it is. + */ +static unsigned int sane_fdtable_size(struct fdtable *fdt, unsigned int max_fds) +{ + unsigned int count; + + count = count_open_files(fdt); + if (max_fds < NR_OPEN_DEFAULT) + max_fds = NR_OPEN_DEFAULT; + return ALIGN(min(count, max_fds), BITS_PER_LONG); +} + +/* + * Allocate a new files structure and copy contents from the + * passed in files structure. + * errorp will be valid only when the returned files_struct is NULL. + */ +struct files_struct *dup_fd(struct files_struct *oldf, unsigned int max_fds, int *errorp) +{ + struct files_struct *newf; + struct file **old_fds, **new_fds; + unsigned int open_files, i; + struct fdtable *old_fdt, *new_fdt; + + *errorp = -ENOMEM; + newf = kmem_cache_alloc(files_cachep, GFP_KERNEL); + if (!newf) + goto out; + + atomic_set(&newf->count, 1); + + spin_lock_init(&newf->file_lock); + newf->resize_in_progress = false; + init_waitqueue_head(&newf->resize_wait); + newf->next_fd = 0; + new_fdt = &newf->fdtab; + new_fdt->max_fds = NR_OPEN_DEFAULT; + new_fdt->close_on_exec = newf->close_on_exec_init; + new_fdt->open_fds = newf->open_fds_init; + new_fdt->full_fds_bits = newf->full_fds_bits_init; + new_fdt->fd = &newf->fd_array[0]; + + spin_lock(&oldf->file_lock); + old_fdt = files_fdtable(oldf); + open_files = sane_fdtable_size(old_fdt, max_fds); + + /* + * Check whether we need to allocate a larger fd array and fd set. + */ + while (unlikely(open_files > new_fdt->max_fds)) { + spin_unlock(&oldf->file_lock); + + if (new_fdt != &newf->fdtab) + __free_fdtable(new_fdt); + + new_fdt = alloc_fdtable(open_files - 1); + if (!new_fdt) { + *errorp = -ENOMEM; + goto out_release; + } + + /* beyond sysctl_nr_open; nothing to do */ + if (unlikely(new_fdt->max_fds < open_files)) { + __free_fdtable(new_fdt); + *errorp = -EMFILE; + goto out_release; + } + + /* + * Reacquire the oldf lock and a pointer to its fd table + * who knows it may have a new bigger fd table. We need + * the latest pointer. + */ + spin_lock(&oldf->file_lock); + old_fdt = files_fdtable(oldf); + open_files = sane_fdtable_size(old_fdt, max_fds); + } + + copy_fd_bitmaps(new_fdt, old_fdt, open_files); + + old_fds = old_fdt->fd; + new_fds = new_fdt->fd; + + for (i = open_files; i != 0; i--) { + struct file *f = *old_fds++; + if (f) { + get_file(f); + } else { + /* + * The fd may be claimed in the fd bitmap but not yet + * instantiated in the files array if a sibling thread + * is partway through open(). So make sure that this + * fd is available to the new process. + */ + __clear_open_fd(open_files - i, new_fdt); + } + rcu_assign_pointer(*new_fds++, f); + } + spin_unlock(&oldf->file_lock); + + /* clear the remainder */ + memset(new_fds, 0, (new_fdt->max_fds - open_files) * sizeof(struct file *)); + + rcu_assign_pointer(newf->fdt, new_fdt); + + return newf; + +out_release: + kmem_cache_free(files_cachep, newf); +out: + return NULL; +} + +static struct fdtable *close_files(struct files_struct * files) +{ + /* + * It is safe to dereference the fd table without RCU or + * ->file_lock because this is the last reference to the + * files structure. + */ + struct fdtable *fdt = rcu_dereference_raw(files->fdt); + unsigned int i, j = 0; + + for (;;) { + unsigned long set; + i = j * BITS_PER_LONG; + if (i >= fdt->max_fds) + break; + set = fdt->open_fds[j++]; + while (set) { + if (set & 1) { + struct file * file = xchg(&fdt->fd[i], NULL); + if (file) { + filp_close(file, files); + cond_resched(); + } + } + i++; + set >>= 1; + } + } + + return fdt; +} + +void put_files_struct(struct files_struct *files) +{ + if (atomic_dec_and_test(&files->count)) { + struct fdtable *fdt = close_files(files); + + /* free the arrays if they are not embedded */ + if (fdt != &files->fdtab) + __free_fdtable(fdt); + kmem_cache_free(files_cachep, files); + } +} + +void exit_files(struct task_struct *tsk) +{ + struct files_struct * files = tsk->files; + + if (files) { + task_lock(tsk); + tsk->files = NULL; + task_unlock(tsk); + put_files_struct(files); + } +} + +struct files_struct init_files = { + .count = ATOMIC_INIT(1), + .fdt = &init_files.fdtab, + .fdtab = { + .max_fds = NR_OPEN_DEFAULT, + .fd = &init_files.fd_array[0], + .close_on_exec = init_files.close_on_exec_init, + .open_fds = init_files.open_fds_init, + .full_fds_bits = init_files.full_fds_bits_init, + }, + .file_lock = __SPIN_LOCK_UNLOCKED(init_files.file_lock), + .resize_wait = __WAIT_QUEUE_HEAD_INITIALIZER(init_files.resize_wait), +}; + +static unsigned int find_next_fd(struct fdtable *fdt, unsigned int start) +{ + unsigned int maxfd = fdt->max_fds; + unsigned int maxbit = maxfd / BITS_PER_LONG; + unsigned int bitbit = start / BITS_PER_LONG; + + bitbit = find_next_zero_bit(fdt->full_fds_bits, maxbit, bitbit) * BITS_PER_LONG; + if (bitbit > maxfd) + return maxfd; + if (bitbit > start) + start = bitbit; + return find_next_zero_bit(fdt->open_fds, maxfd, start); +} + +/* + * allocate a file descriptor, mark it busy. + */ +static int alloc_fd(unsigned start, unsigned end, unsigned flags) +{ + struct files_struct *files = current->files; + unsigned int fd; + int error; + struct fdtable *fdt; + + spin_lock(&files->file_lock); +repeat: + fdt = files_fdtable(files); + fd = start; + if (fd < files->next_fd) + fd = files->next_fd; + + if (fd < fdt->max_fds) + fd = find_next_fd(fdt, fd); + + /* + * N.B. For clone tasks sharing a files structure, this test + * will limit the total number of files that can be opened. + */ + error = -EMFILE; + if (fd >= end) + goto out; + + error = expand_files(files, fd); + if (error < 0) + goto out; + + /* + * If we needed to expand the fs array we + * might have blocked - try again. + */ + if (error) + goto repeat; + + if (start <= files->next_fd) + files->next_fd = fd + 1; + + __set_open_fd(fd, fdt); + if (flags & O_CLOEXEC) + __set_close_on_exec(fd, fdt); + else + __clear_close_on_exec(fd, fdt); + error = fd; +#if 1 + /* Sanity check */ + if (rcu_access_pointer(fdt->fd[fd]) != NULL) { + printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd); + rcu_assign_pointer(fdt->fd[fd], NULL); + } +#endif + +out: + spin_unlock(&files->file_lock); + return error; +} + +int __get_unused_fd_flags(unsigned flags, unsigned long nofile) +{ + return alloc_fd(0, nofile, flags); +} + +int get_unused_fd_flags(unsigned flags) +{ + return __get_unused_fd_flags(flags, rlimit(RLIMIT_NOFILE)); +} +EXPORT_SYMBOL(get_unused_fd_flags); + +static void __put_unused_fd(struct files_struct *files, unsigned int fd) +{ + struct fdtable *fdt = files_fdtable(files); + __clear_open_fd(fd, fdt); + if (fd < files->next_fd) + files->next_fd = fd; +} + +void put_unused_fd(unsigned int fd) +{ + struct files_struct *files = current->files; + spin_lock(&files->file_lock); + __put_unused_fd(files, fd); + spin_unlock(&files->file_lock); +} + +EXPORT_SYMBOL(put_unused_fd); + +/* + * Install a file pointer in the fd array. + * + * The VFS is full of places where we drop the files lock between + * setting the open_fds bitmap and installing the file in the file + * array. At any such point, we are vulnerable to a dup2() race + * installing a file in the array before us. We need to detect this and + * fput() the struct file we are about to overwrite in this case. + * + * It should never happen - if we allow dup2() do it, _really_ bad things + * will follow. + * + * This consumes the "file" refcount, so callers should treat it + * as if they had called fput(file). + */ + +void fd_install(unsigned int fd, struct file *file) +{ + struct files_struct *files = current->files; + struct fdtable *fdt; + + rcu_read_lock_sched(); + + if (unlikely(files->resize_in_progress)) { + rcu_read_unlock_sched(); + spin_lock(&files->file_lock); + fdt = files_fdtable(files); + BUG_ON(fdt->fd[fd] != NULL); + rcu_assign_pointer(fdt->fd[fd], file); + spin_unlock(&files->file_lock); + return; + } + /* coupled with smp_wmb() in expand_fdtable() */ + smp_rmb(); + fdt = rcu_dereference_sched(files->fdt); + BUG_ON(fdt->fd[fd] != NULL); + rcu_assign_pointer(fdt->fd[fd], file); + rcu_read_unlock_sched(); +} + +EXPORT_SYMBOL(fd_install); + +/** + * pick_file - return file associatd with fd + * @files: file struct to retrieve file from + * @fd: file descriptor to retrieve file for + * + * Context: files_lock must be held. + * + * Returns: The file associated with @fd (NULL if @fd is not open) + */ +static struct file *pick_file(struct files_struct *files, unsigned fd) +{ + struct fdtable *fdt = files_fdtable(files); + struct file *file; + + if (fd >= fdt->max_fds) + return NULL; + + fd = array_index_nospec(fd, fdt->max_fds); + file = fdt->fd[fd]; + if (file) { + rcu_assign_pointer(fdt->fd[fd], NULL); + __put_unused_fd(files, fd); + } + return file; +} + +int close_fd(unsigned fd) +{ + struct files_struct *files = current->files; + struct file *file; + + spin_lock(&files->file_lock); + file = pick_file(files, fd); + spin_unlock(&files->file_lock); + if (!file) + return -EBADF; + + return filp_close(file, files); +} +EXPORT_SYMBOL(close_fd); /* for ksys_close() */ + +/** + * last_fd - return last valid index into fd table + * @fdt: File descriptor table. + * + * Context: Either rcu read lock or files_lock must be held. + * + * Returns: Last valid index into fdtable. + */ +static inline unsigned last_fd(struct fdtable *fdt) +{ + return fdt->max_fds - 1; +} + +static inline void __range_cloexec(struct files_struct *cur_fds, + unsigned int fd, unsigned int max_fd) +{ + struct fdtable *fdt; + + /* make sure we're using the correct maximum value */ + spin_lock(&cur_fds->file_lock); + fdt = files_fdtable(cur_fds); + max_fd = min(last_fd(fdt), max_fd); + if (fd <= max_fd) + bitmap_set(fdt->close_on_exec, fd, max_fd - fd + 1); + spin_unlock(&cur_fds->file_lock); +} + +static inline void __range_close(struct files_struct *files, unsigned int fd, + unsigned int max_fd) +{ + struct file *file; + unsigned n; + + spin_lock(&files->file_lock); + n = last_fd(files_fdtable(files)); + max_fd = min(max_fd, n); + + for (; fd <= max_fd; fd++) { + file = pick_file(files, fd); + if (file) { + spin_unlock(&files->file_lock); + filp_close(file, files); + cond_resched(); + spin_lock(&files->file_lock); + } else if (need_resched()) { + spin_unlock(&files->file_lock); + cond_resched(); + spin_lock(&files->file_lock); + } + } + spin_unlock(&files->file_lock); +} + +/** + * __close_range() - Close all file descriptors in a given range. + * + * @fd: starting file descriptor to close + * @max_fd: last file descriptor to close + * @flags: CLOSE_RANGE flags. + * + * This closes a range of file descriptors. All file descriptors + * from @fd up to and including @max_fd are closed. + */ +int __close_range(unsigned fd, unsigned max_fd, unsigned int flags) +{ + struct task_struct *me = current; + struct files_struct *cur_fds = me->files, *fds = NULL; + + if (flags & ~(CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC)) + return -EINVAL; + + if (fd > max_fd) + return -EINVAL; + + if (flags & CLOSE_RANGE_UNSHARE) { + int ret; + unsigned int max_unshare_fds = NR_OPEN_MAX; + + /* + * If the caller requested all fds to be made cloexec we always + * copy all of the file descriptors since they still want to + * use them. + */ + if (!(flags & CLOSE_RANGE_CLOEXEC)) { + /* + * If the requested range is greater than the current + * maximum, we're closing everything so only copy all + * file descriptors beneath the lowest file descriptor. + */ + rcu_read_lock(); + if (max_fd >= last_fd(files_fdtable(cur_fds))) + max_unshare_fds = fd; + rcu_read_unlock(); + } + + ret = unshare_fd(CLONE_FILES, max_unshare_fds, &fds); + if (ret) + return ret; + + /* + * We used to share our file descriptor table, and have now + * created a private one, make sure we're using it below. + */ + if (fds) + swap(cur_fds, fds); + } + + if (flags & CLOSE_RANGE_CLOEXEC) + __range_cloexec(cur_fds, fd, max_fd); + else + __range_close(cur_fds, fd, max_fd); + + if (fds) { + /* + * We're done closing the files we were supposed to. Time to install + * the new file descriptor table and drop the old one. + */ + task_lock(me); + me->files = cur_fds; + task_unlock(me); + put_files_struct(fds); + } + + return 0; +} + +/* + * See close_fd_get_file() below, this variant assumes current->files->file_lock + * is held. + */ +struct file *__close_fd_get_file(unsigned int fd) +{ + return pick_file(current->files, fd); +} + +/* + * variant of close_fd that gets a ref on the file for later fput. + * The caller must ensure that filp_close() called on the file. + */ +struct file *close_fd_get_file(unsigned int fd) +{ + struct files_struct *files = current->files; + struct file *file; + + spin_lock(&files->file_lock); + file = pick_file(files, fd); + spin_unlock(&files->file_lock); + + return file; +} + +void do_close_on_exec(struct files_struct *files) +{ + unsigned i; + struct fdtable *fdt; + + /* exec unshares first */ + spin_lock(&files->file_lock); + for (i = 0; ; i++) { + unsigned long set; + unsigned fd = i * BITS_PER_LONG; + fdt = files_fdtable(files); + if (fd >= fdt->max_fds) + break; + set = fdt->close_on_exec[i]; + if (!set) + continue; + fdt->close_on_exec[i] = 0; + for ( ; set ; fd++, set >>= 1) { + struct file *file; + if (!(set & 1)) + continue; + file = fdt->fd[fd]; + if (!file) + continue; + rcu_assign_pointer(fdt->fd[fd], NULL); + __put_unused_fd(files, fd); + spin_unlock(&files->file_lock); + filp_close(file, files); + cond_resched(); + spin_lock(&files->file_lock); + } + + } + spin_unlock(&files->file_lock); +} + +static inline struct file *__fget_files_rcu(struct files_struct *files, + unsigned int fd, fmode_t mask) +{ + for (;;) { + struct file *file; + struct fdtable *fdt = rcu_dereference_raw(files->fdt); + struct file __rcu **fdentry; + + if (unlikely(fd >= fdt->max_fds)) + return NULL; + + fdentry = fdt->fd + array_index_nospec(fd, fdt->max_fds); + file = rcu_dereference_raw(*fdentry); + if (unlikely(!file)) + return NULL; + + if (unlikely(file->f_mode & mask)) + return NULL; + + /* + * Ok, we have a file pointer. However, because we do + * this all locklessly under RCU, we may be racing with + * that file being closed. + * + * Such a race can take two forms: + * + * (a) the file ref already went down to zero, + * and get_file_rcu() fails. Just try again: + */ + if (unlikely(!get_file_rcu(file))) + continue; + + /* + * (b) the file table entry has changed under us. + * Note that we don't need to re-check the 'fdt->fd' + * pointer having changed, because it always goes + * hand-in-hand with 'fdt'. + * + * If so, we need to put our ref and try again. + */ + if (unlikely(rcu_dereference_raw(files->fdt) != fdt) || + unlikely(rcu_dereference_raw(*fdentry) != file)) { + fput(file); + continue; + } + + /* + * Ok, we have a ref to the file, and checked that it + * still exists. + */ + return file; + } +} + +static struct file *__fget_files(struct files_struct *files, unsigned int fd, + fmode_t mask) +{ + struct file *file; + + rcu_read_lock(); + file = __fget_files_rcu(files, fd, mask); + rcu_read_unlock(); + + return file; +} + +static inline struct file *__fget(unsigned int fd, fmode_t mask) +{ + return __fget_files(current->files, fd, mask); +} + +struct file *fget(unsigned int fd) +{ + return __fget(fd, FMODE_PATH); +} +EXPORT_SYMBOL(fget); + +struct file *fget_raw(unsigned int fd) +{ + return __fget(fd, 0); +} +EXPORT_SYMBOL(fget_raw); + +struct file *fget_task(struct task_struct *task, unsigned int fd) +{ + struct file *file = NULL; + + task_lock(task); + if (task->files) + file = __fget_files(task->files, fd, 0); + task_unlock(task); + + return file; +} + +struct file *task_lookup_fd_rcu(struct task_struct *task, unsigned int fd) +{ + /* Must be called with rcu_read_lock held */ + struct files_struct *files; + struct file *file = NULL; + + task_lock(task); + files = task->files; + if (files) + file = files_lookup_fd_rcu(files, fd); + task_unlock(task); + + return file; +} + +struct file *task_lookup_next_fd_rcu(struct task_struct *task, unsigned int *ret_fd) +{ + /* Must be called with rcu_read_lock held */ + struct files_struct *files; + unsigned int fd = *ret_fd; + struct file *file = NULL; + + task_lock(task); + files = task->files; + if (files) { + for (; fd < files_fdtable(files)->max_fds; fd++) { + file = files_lookup_fd_rcu(files, fd); + if (file) + break; + } + } + task_unlock(task); + *ret_fd = fd; + return file; +} +EXPORT_SYMBOL(task_lookup_next_fd_rcu); + +/* + * Lightweight file lookup - no refcnt increment if fd table isn't shared. + * + * You can use this instead of fget if you satisfy all of the following + * conditions: + * 1) You must call fput_light before exiting the syscall and returning control + * to userspace (i.e. you cannot remember the returned struct file * after + * returning to userspace). + * 2) You must not call filp_close on the returned struct file * in between + * calls to fget_light and fput_light. + * 3) You must not clone the current task in between the calls to fget_light + * and fput_light. + * + * The fput_needed flag returned by fget_light should be passed to the + * corresponding fput_light. + */ +static unsigned long __fget_light(unsigned int fd, fmode_t mask) +{ + struct files_struct *files = current->files; + struct file *file; + + /* + * If another thread is concurrently calling close_fd() followed + * by put_files_struct(), we must not observe the old table + * entry combined with the new refcount - otherwise we could + * return a file that is concurrently being freed. + * + * atomic_read_acquire() pairs with atomic_dec_and_test() in + * put_files_struct(). + */ + if (atomic_read_acquire(&files->count) == 1) { + file = files_lookup_fd_raw(files, fd); + if (!file || unlikely(file->f_mode & mask)) + return 0; + return (unsigned long)file; + } else { + file = __fget(fd, mask); + if (!file) + return 0; + return FDPUT_FPUT | (unsigned long)file; + } +} +unsigned long __fdget(unsigned int fd) +{ + return __fget_light(fd, FMODE_PATH); +} +EXPORT_SYMBOL(__fdget); + +unsigned long __fdget_raw(unsigned int fd) +{ + return __fget_light(fd, 0); +} + +/* + * Try to avoid f_pos locking. We only need it if the + * file is marked for FMODE_ATOMIC_POS, and it can be + * accessed multiple ways. + * + * Always do it for directories, because pidfd_getfd() + * can make a file accessible even if it otherwise would + * not be, and for directories this is a correctness + * issue, not a "POSIX requirement". + */ +static inline bool file_needs_f_pos_lock(struct file *file) +{ + return (file->f_mode & FMODE_ATOMIC_POS) && + (file_count(file) > 1 || file->f_op->iterate_shared); +} + +unsigned long __fdget_pos(unsigned int fd) +{ + unsigned long v = __fdget(fd); + struct file *file = (struct file *)(v & ~3); + + if (file && file_needs_f_pos_lock(file)) { + v |= FDPUT_POS_UNLOCK; + mutex_lock(&file->f_pos_lock); + } + return v; +} + +void __f_unlock_pos(struct file *f) +{ + mutex_unlock(&f->f_pos_lock); +} + +/* + * We only lock f_pos if we have threads or if the file might be + * shared with another process. In both cases we'll have an elevated + * file count (done either by fdget() or by fork()). + */ + +void set_close_on_exec(unsigned int fd, int flag) +{ + struct files_struct *files = current->files; + struct fdtable *fdt; + spin_lock(&files->file_lock); + fdt = files_fdtable(files); + if (flag) + __set_close_on_exec(fd, fdt); + else + __clear_close_on_exec(fd, fdt); + spin_unlock(&files->file_lock); +} + +bool get_close_on_exec(unsigned int fd) +{ + struct files_struct *files = current->files; + struct fdtable *fdt; + bool res; + rcu_read_lock(); + fdt = files_fdtable(files); + res = close_on_exec(fd, fdt); + rcu_read_unlock(); + return res; +} + +static int do_dup2(struct files_struct *files, + struct file *file, unsigned fd, unsigned flags) +__releases(&files->file_lock) +{ + struct file *tofree; + struct fdtable *fdt; + + /* + * We need to detect attempts to do dup2() over allocated but still + * not finished descriptor. NB: OpenBSD avoids that at the price of + * extra work in their equivalent of fget() - they insert struct + * file immediately after grabbing descriptor, mark it larval if + * more work (e.g. actual opening) is needed and make sure that + * fget() treats larval files as absent. Potentially interesting, + * but while extra work in fget() is trivial, locking implications + * and amount of surgery on open()-related paths in VFS are not. + * FreeBSD fails with -EBADF in the same situation, NetBSD "solution" + * deadlocks in rather amusing ways, AFAICS. All of that is out of + * scope of POSIX or SUS, since neither considers shared descriptor + * tables and this condition does not arise without those. + */ + fdt = files_fdtable(files); + tofree = fdt->fd[fd]; + if (!tofree && fd_is_open(fd, fdt)) + goto Ebusy; + get_file(file); + rcu_assign_pointer(fdt->fd[fd], file); + __set_open_fd(fd, fdt); + if (flags & O_CLOEXEC) + __set_close_on_exec(fd, fdt); + else + __clear_close_on_exec(fd, fdt); + spin_unlock(&files->file_lock); + + if (tofree) + filp_close(tofree, files); + + return fd; + +Ebusy: + spin_unlock(&files->file_lock); + return -EBUSY; +} + +int replace_fd(unsigned fd, struct file *file, unsigned flags) +{ + int err; + struct files_struct *files = current->files; + + if (!file) + return close_fd(fd); + + if (fd >= rlimit(RLIMIT_NOFILE)) + return -EBADF; + + spin_lock(&files->file_lock); + err = expand_files(files, fd); + if (unlikely(err < 0)) + goto out_unlock; + return do_dup2(files, file, fd, flags); + +out_unlock: + spin_unlock(&files->file_lock); + return err; +} + +/** + * __receive_fd() - Install received file into file descriptor table + * @file: struct file that was received from another process + * @ufd: __user pointer to write new fd number to + * @o_flags: the O_* flags to apply to the new fd entry + * + * Installs a received file into the file descriptor table, with appropriate + * checks and count updates. Optionally writes the fd number to userspace, if + * @ufd is non-NULL. + * + * This helper handles its own reference counting of the incoming + * struct file. + * + * Returns newly install fd or -ve on error. + */ +int __receive_fd(struct file *file, int __user *ufd, unsigned int o_flags) +{ + int new_fd; + int error; + + error = security_file_receive(file); + if (error) + return error; + + new_fd = get_unused_fd_flags(o_flags); + if (new_fd < 0) + return new_fd; + + if (ufd) { + error = put_user(new_fd, ufd); + if (error) { + put_unused_fd(new_fd); + return error; + } + } + + fd_install(new_fd, get_file(file)); + __receive_sock(file); + return new_fd; +} + +int receive_fd_replace(int new_fd, struct file *file, unsigned int o_flags) +{ + int error; + + error = security_file_receive(file); + if (error) + return error; + error = replace_fd(new_fd, file, o_flags); + if (error) + return error; + __receive_sock(file); + return new_fd; +} + +int receive_fd(struct file *file, unsigned int o_flags) +{ + return __receive_fd(file, NULL, o_flags); +} +EXPORT_SYMBOL_GPL(receive_fd); + +static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags) +{ + int err = -EBADF; + struct file *file; + struct files_struct *files = current->files; + + if ((flags & ~O_CLOEXEC) != 0) + return -EINVAL; + + if (unlikely(oldfd == newfd)) + return -EINVAL; + + if (newfd >= rlimit(RLIMIT_NOFILE)) + return -EBADF; + + spin_lock(&files->file_lock); + err = expand_files(files, newfd); + file = files_lookup_fd_locked(files, oldfd); + if (unlikely(!file)) + goto Ebadf; + if (unlikely(err < 0)) { + if (err == -EMFILE) + goto Ebadf; + goto out_unlock; + } + return do_dup2(files, file, newfd, flags); + +Ebadf: + err = -EBADF; +out_unlock: + spin_unlock(&files->file_lock); + return err; +} + +SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags) +{ + return ksys_dup3(oldfd, newfd, flags); +} + +SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd) +{ + if (unlikely(newfd == oldfd)) { /* corner case */ + struct files_struct *files = current->files; + int retval = oldfd; + + rcu_read_lock(); + if (!files_lookup_fd_rcu(files, oldfd)) + retval = -EBADF; + rcu_read_unlock(); + return retval; + } + return ksys_dup3(oldfd, newfd, 0); +} + +SYSCALL_DEFINE1(dup, unsigned int, fildes) +{ + int ret = -EBADF; + struct file *file = fget_raw(fildes); + + if (file) { + ret = get_unused_fd_flags(0); + if (ret >= 0) + fd_install(ret, file); + else + fput(file); + } + return ret; +} + +int f_dupfd(unsigned int from, struct file *file, unsigned flags) +{ + unsigned long nofile = rlimit(RLIMIT_NOFILE); + int err; + if (from >= nofile) + return -EINVAL; + err = alloc_fd(from, nofile, flags); + if (err >= 0) { + get_file(file); + fd_install(err, file); + } + return err; +} + +int iterate_fd(struct files_struct *files, unsigned n, + int (*f)(const void *, struct file *, unsigned), + const void *p) +{ + struct fdtable *fdt; + int res = 0; + if (!files) + return 0; + spin_lock(&files->file_lock); + for (fdt = files_fdtable(files); n < fdt->max_fds; n++) { + struct file *file; + file = rcu_dereference_check_fdtable(files, fdt->fd[n]); + if (!file) + continue; + res = f(p, file, n); + if (res) + break; + } + spin_unlock(&files->file_lock); + return res; +} +EXPORT_SYMBOL(iterate_fd); |