Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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);
+}