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/* 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 */
#define DATA_FD_MEMORY_LIMIT (64U * U64_KB)
/* If memfd 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 (1U * U64_MB)
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(). 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 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) || (uint64_t) st.st_size < DATA_FD_MEMORY_LIMIT) {
/* Try a memfd first */
copy_fd = memfd_new("data-fd");
if (copy_fd < 0)
return copy_fd;
r = copy_bytes(fd, copy_fd, DATA_FD_MEMORY_LIMIT, COPY_REFLINK);
if (r < 0)
return r;
off_t f = lseek(copy_fd, 0, SEEK_SET);
if (f < 0)
return -errno;
if (f != 0)
return -EIO;
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);
}
}
/* If we have reason to believe this will fit fine in /tmp, then use that as first fallback. */
if ((!S_ISREG(st.st_mode) || (uint64_t) st.st_size < DATA_FD_TMP_LIMIT) &&
(DATA_FD_MEMORY_LIMIT + remains_size) < DATA_FD_TMP_LIMIT) {
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 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, COPY_REFLINK);
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 */
off_t f = lseek(tmp_fd, 0, SEEK_SET);
if (f < 0)
return -errno;
if (f != 0)
return -EIO;
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 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);
}
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