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-rw-r--r--src/shared/data-fd-util.c391
1 files changed, 391 insertions, 0 deletions
diff --git a/src/shared/data-fd-util.c b/src/shared/data-fd-util.c
new file mode 100644
index 0000000..b939206
--- /dev/null
+++ b/src/shared/data-fd-util.c
@@ -0,0 +1,391 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#if HAVE_LINUX_MEMFD_H
+#include <linux/memfd.h>
+#endif
+
+#include "alloc-util.h"
+#include "copy.h"
+#include "data-fd-util.h"
+#include "fd-util.h"
+#include "fs-util.h"
+#include "io-util.h"
+#include "memfd-util.h"
+#include "missing_mman.h"
+#include "missing_syscall.h"
+#include "tmpfile-util.h"
+
+/* When the data is smaller or equal to 64K, try to place the copy in a memfd/pipe */
+#define DATA_FD_MEMORY_LIMIT (64U*1024U)
+
+/* If memfd/pipe didn't work out, then let's use a file in /tmp up to a size of 1M. If it's large than that use /var/tmp instead. */
+#define DATA_FD_TMP_LIMIT (1024U*1024U)
+
+int acquire_data_fd(const void *data, size_t size, unsigned flags) {
+ _cleanup_close_pair_ int pipefds[2] = EBADF_PAIR;
+ _cleanup_close_ int fd = -EBADF;
+ int isz = 0, r;
+ ssize_t n;
+
+ assert(data || size == 0);
+
+ /* Acquire a read-only file descriptor that when read from returns the specified data. This is much more
+ * complex than I wish it was. But here's why:
+ *
+ * a) First we try to use memfds. They are the best option, as we can seal them nicely to make them
+ * read-only. Unfortunately they require kernel 3.17, and – at the time of writing – we still support 3.14.
+ *
+ * b) Then, we try classic pipes. They are the second best options, as we can close the writing side, retaining
+ * a nicely read-only fd in the reading side. However, they are by default quite small, and unprivileged
+ * clients can only bump their size to a system-wide limit, which might be quite low.
+ *
+ * c) Then, we try an O_TMPFILE file in /dev/shm (that dir is the only suitable one known to exist from
+ * earliest boot on). To make it read-only we open the fd a second time with O_RDONLY via
+ * /proc/self/<fd>. Unfortunately O_TMPFILE is not available on older kernels on tmpfs.
+ *
+ * d) Finally, we try creating a regular file in /dev/shm, which we then delete.
+ *
+ * It sucks a bit that depending on the situation we return very different objects here, but that's Linux I
+ * figure. */
+
+ if (size == 0 && ((flags & ACQUIRE_NO_DEV_NULL) == 0))
+ /* As a special case, return /dev/null if we have been called for an empty data block */
+ return RET_NERRNO(open("/dev/null", O_RDONLY|O_CLOEXEC|O_NOCTTY));
+
+ if ((flags & ACQUIRE_NO_MEMFD) == 0) {
+ fd = memfd_new_and_seal("data-fd", data, size);
+ if (fd < 0) {
+ if (ERRNO_IS_NOT_SUPPORTED(fd))
+ goto try_pipe;
+
+ return fd;
+ }
+
+ return TAKE_FD(fd);
+ }
+
+try_pipe:
+ if ((flags & ACQUIRE_NO_PIPE) == 0) {
+ if (pipe2(pipefds, O_CLOEXEC|O_NONBLOCK) < 0)
+ return -errno;
+
+ isz = fcntl(pipefds[1], F_GETPIPE_SZ, 0);
+ if (isz < 0)
+ return -errno;
+
+ if ((size_t) isz < size) {
+ isz = (int) size;
+ if (isz < 0 || (size_t) isz != size)
+ return -E2BIG;
+
+ /* Try to bump the pipe size */
+ (void) fcntl(pipefds[1], F_SETPIPE_SZ, isz);
+
+ /* See if that worked */
+ isz = fcntl(pipefds[1], F_GETPIPE_SZ, 0);
+ if (isz < 0)
+ return -errno;
+
+ if ((size_t) isz < size)
+ goto try_dev_shm;
+ }
+
+ n = write(pipefds[1], data, size);
+ if (n < 0)
+ return -errno;
+ if ((size_t) n != size)
+ return -EIO;
+
+ (void) fd_nonblock(pipefds[0], false);
+
+ return TAKE_FD(pipefds[0]);
+ }
+
+try_dev_shm:
+ if ((flags & ACQUIRE_NO_TMPFILE) == 0) {
+ fd = open("/dev/shm", O_RDWR|O_TMPFILE|O_CLOEXEC, 0500);
+ if (fd < 0)
+ goto try_dev_shm_without_o_tmpfile;
+
+ n = write(fd, data, size);
+ if (n < 0)
+ return -errno;
+ if ((size_t) n != size)
+ return -EIO;
+
+ /* Let's reopen the thing, in order to get an O_RDONLY fd for the original O_RDWR one */
+ return fd_reopen(fd, O_RDONLY|O_CLOEXEC);
+ }
+
+try_dev_shm_without_o_tmpfile:
+ if ((flags & ACQUIRE_NO_REGULAR) == 0) {
+ char pattern[] = "/dev/shm/data-fd-XXXXXX";
+
+ fd = mkostemp_safe(pattern);
+ if (fd < 0)
+ return fd;
+
+ n = write(fd, data, size);
+ if (n < 0) {
+ r = -errno;
+ goto unlink_and_return;
+ }
+ if ((size_t) n != size) {
+ r = -EIO;
+ goto unlink_and_return;
+ }
+
+ /* Let's reopen the thing, in order to get an O_RDONLY fd for the original O_RDWR one */
+ r = fd_reopen(fd, O_RDONLY|O_CLOEXEC);
+
+ unlink_and_return:
+ (void) unlink(pattern);
+ return r;
+ }
+
+ return -EOPNOTSUPP;
+}
+
+int copy_data_fd(int fd) {
+ _cleanup_close_ int copy_fd = -EBADF, tmp_fd = -EBADF;
+ _cleanup_free_ void *remains = NULL;
+ size_t remains_size = 0;
+ const char *td;
+ struct stat st;
+ int r;
+
+ /* Creates a 'data' fd from the specified source fd, containing all the same data in a read-only fashion, but
+ * independent of it (i.e. the source fd can be closed and unmounted after this call succeeded). Tries to be
+ * somewhat smart about where to place the data. In the best case uses a memfd(). If memfd() are not supported
+ * uses a pipe instead. For larger data will use an unlinked file in /tmp, and for even larger data one in
+ * /var/tmp. */
+
+ if (fstat(fd, &st) < 0)
+ return -errno;
+
+ /* For now, let's only accept regular files, sockets, pipes and char devices */
+ if (S_ISDIR(st.st_mode))
+ return -EISDIR;
+ if (S_ISLNK(st.st_mode))
+ return -ELOOP;
+ if (!S_ISREG(st.st_mode) && !S_ISSOCK(st.st_mode) && !S_ISFIFO(st.st_mode) && !S_ISCHR(st.st_mode))
+ return -EBADFD;
+
+ /* If we have reason to believe the data is bounded in size, then let's use memfds or pipes as backing fd. Note
+ * that we use the reported regular file size only as a hint, given that there are plenty special files in
+ * /proc and /sys which report a zero file size but can be read from. */
+
+ if (!S_ISREG(st.st_mode) || st.st_size < DATA_FD_MEMORY_LIMIT) {
+
+ /* Try a memfd first */
+ copy_fd = memfd_new("data-fd");
+ if (copy_fd >= 0) {
+ off_t f;
+
+ r = copy_bytes(fd, copy_fd, DATA_FD_MEMORY_LIMIT, 0);
+ if (r < 0)
+ return r;
+
+ f = lseek(copy_fd, 0, SEEK_SET);
+ if (f != 0)
+ return -errno;
+
+ if (r == 0) {
+ /* Did it fit into the limit? If so, we are done. */
+ r = memfd_set_sealed(copy_fd);
+ if (r < 0)
+ return r;
+
+ return TAKE_FD(copy_fd);
+ }
+
+ /* Hmm, pity, this didn't fit. Let's fall back to /tmp then, see below */
+
+ } else {
+ _cleanup_close_pair_ int pipefds[2] = EBADF_PAIR;
+ int isz;
+
+ /* If memfds aren't available, use a pipe. Set O_NONBLOCK so that we will get EAGAIN rather
+ * then block indefinitely when we hit the pipe size limit */
+
+ if (pipe2(pipefds, O_CLOEXEC|O_NONBLOCK) < 0)
+ return -errno;
+
+ isz = fcntl(pipefds[1], F_GETPIPE_SZ, 0);
+ if (isz < 0)
+ return -errno;
+
+ /* Try to enlarge the pipe size if necessary */
+ if ((size_t) isz < DATA_FD_MEMORY_LIMIT) {
+
+ (void) fcntl(pipefds[1], F_SETPIPE_SZ, DATA_FD_MEMORY_LIMIT);
+
+ isz = fcntl(pipefds[1], F_GETPIPE_SZ, 0);
+ if (isz < 0)
+ return -errno;
+ }
+
+ if ((size_t) isz >= DATA_FD_MEMORY_LIMIT) {
+
+ r = copy_bytes_full(fd, pipefds[1], DATA_FD_MEMORY_LIMIT, 0, &remains, &remains_size, NULL, NULL);
+ if (r < 0 && r != -EAGAIN)
+ return r; /* If we get EAGAIN it could be because of the source or because of
+ * the destination fd, we can't know, as sendfile() and friends won't
+ * tell us. Hence, treat this as reason to fall back, just to be
+ * sure. */
+ if (r == 0) {
+ /* Everything fit in, yay! */
+ (void) fd_nonblock(pipefds[0], false);
+
+ return TAKE_FD(pipefds[0]);
+ }
+
+ /* Things didn't fit in. But we read data into the pipe, let's remember that, so that
+ * when writing the new file we incorporate this first. */
+ copy_fd = TAKE_FD(pipefds[0]);
+ }
+ }
+ }
+
+ /* If we have reason to believe this will fit fine in /tmp, then use that as first fallback. */
+ if ((!S_ISREG(st.st_mode) || st.st_size < DATA_FD_TMP_LIMIT) &&
+ (DATA_FD_MEMORY_LIMIT + remains_size) < DATA_FD_TMP_LIMIT) {
+ off_t f;
+
+ tmp_fd = open_tmpfile_unlinkable(NULL /* NULL as directory means /tmp */, O_RDWR|O_CLOEXEC);
+ if (tmp_fd < 0)
+ return tmp_fd;
+
+ if (copy_fd >= 0) {
+ /* If we tried a memfd/pipe first and it ended up being too large, then copy this into the
+ * temporary file first. */
+
+ r = copy_bytes(copy_fd, tmp_fd, UINT64_MAX, 0);
+ if (r < 0)
+ return r;
+
+ assert(r == 0);
+ }
+
+ if (remains_size > 0) {
+ /* If there were remaining bytes (i.e. read into memory, but not written out yet) from the
+ * failed copy operation, let's flush them out next. */
+
+ r = loop_write(tmp_fd, remains, remains_size);
+ if (r < 0)
+ return r;
+ }
+
+ r = copy_bytes(fd, tmp_fd, DATA_FD_TMP_LIMIT - DATA_FD_MEMORY_LIMIT - remains_size, COPY_REFLINK);
+ if (r < 0)
+ return r;
+ if (r == 0)
+ goto finish; /* Yay, it fit in */
+
+ /* It didn't fit in. Let's not forget to use what we already used */
+ f = lseek(tmp_fd, 0, SEEK_SET);
+ if (f != 0)
+ return -errno;
+
+ close_and_replace(copy_fd, tmp_fd);
+
+ remains = mfree(remains);
+ remains_size = 0;
+ }
+
+ /* As last fallback use /var/tmp */
+ r = var_tmp_dir(&td);
+ if (r < 0)
+ return r;
+
+ tmp_fd = open_tmpfile_unlinkable(td, O_RDWR|O_CLOEXEC);
+ if (tmp_fd < 0)
+ return tmp_fd;
+
+ if (copy_fd >= 0) {
+ /* If we tried a memfd/pipe first, or a file in /tmp, and it ended up being too large, than copy this
+ * into the temporary file first. */
+ r = copy_bytes(copy_fd, tmp_fd, UINT64_MAX, COPY_REFLINK);
+ if (r < 0)
+ return r;
+
+ assert(r == 0);
+ }
+
+ if (remains_size > 0) {
+ /* Then, copy in any read but not yet written bytes. */
+ r = loop_write(tmp_fd, remains, remains_size);
+ if (r < 0)
+ return r;
+ }
+
+ /* Copy in the rest */
+ r = copy_bytes(fd, tmp_fd, UINT64_MAX, COPY_REFLINK);
+ if (r < 0)
+ return r;
+
+ assert(r == 0);
+
+finish:
+ /* Now convert the O_RDWR file descriptor into an O_RDONLY one (and as side effect seek to the beginning of the
+ * file again */
+
+ return fd_reopen(tmp_fd, O_RDONLY|O_CLOEXEC);
+}
+
+int memfd_clone_fd(int fd, const char *name, int mode) {
+ _cleanup_close_ int mfd = -EBADF;
+ struct stat st;
+ bool ro, exec;
+ int r;
+
+ /* Creates a clone of a regular file in a memfd. Unlike copy_data_fd() this returns strictly a memfd
+ * (and if it can't it will fail). Thus the resulting fd is seekable, and definitely reports as
+ * S_ISREG. */
+
+ assert(fd >= 0);
+ assert(name);
+ assert(IN_SET(mode & O_ACCMODE, O_RDONLY, O_RDWR));
+ assert((mode & ~(O_RDONLY|O_RDWR|O_CLOEXEC)) == 0);
+
+ if (fstat(fd, &st) < 0)
+ return -errno;
+
+ ro = (mode & O_ACCMODE) == O_RDONLY;
+ exec = st.st_mode & 0111;
+
+ mfd = memfd_create_wrapper(name,
+ ((FLAGS_SET(mode, O_CLOEXEC) || ro) ? MFD_CLOEXEC : 0) |
+ (ro ? MFD_ALLOW_SEALING : 0) |
+ (exec ? MFD_EXEC : MFD_NOEXEC_SEAL));
+ if (mfd < 0)
+ return mfd;
+
+ r = copy_bytes(fd, mfd, UINT64_MAX, COPY_REFLINK);
+ if (r < 0)
+ return r;
+
+ if (ro) {
+ _cleanup_close_ int rfd = -EBADF;
+
+ r = memfd_set_sealed(mfd);
+ if (r < 0)
+ return r;
+
+ rfd = fd_reopen(mfd, mode);
+ if (rfd < 0)
+ return rfd;
+
+ return TAKE_FD(rfd);
+ }
+
+ off_t f = lseek(mfd, 0, SEEK_SET);
+ if (f < 0)
+ return -errno;
+
+ return TAKE_FD(mfd);
+}