/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include "nm-sd-adapt-shared.h"
#include <errno.h>
#include <fcntl.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <unistd.h>
#include "alloc-util.h"
#include "copy.h"
#include "dirent-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "fs-util.h"
#include "io-util.h"
#include "macro.h"
#include "memfd-util.h"
#include "missing_fcntl.h"
#include "missing_syscall.h"
#include "parse-util.h"
#include "path-util.h"
#include "process-util.h"
#include "socket-util.h"
#include "sort-util.h"
#include "stat-util.h"
#include "stdio-util.h"
#include "tmpfile-util.h"
#include "util.h"
/* The maximum number of iterations in the loop to close descriptors in the fallback case
* when /proc/self/fd/ is inaccessible. */
#define MAX_FD_LOOP_LIMIT (1024*1024)
int close_nointr(int fd) {
assert(fd >= 0);
if (close(fd) >= 0)
return 0;
/*
* Just ignore EINTR; a retry loop is the wrong thing to do on
* Linux.
*
* http://lkml.indiana.edu/hypermail/linux/kernel/0509.1/0877.html
* https://bugzilla.gnome.org/show_bug.cgi?id=682819
* http://utcc.utoronto.ca/~cks/space/blog/unix/CloseEINTR
* https://sites.google.com/site/michaelsafyan/software-engineering/checkforeintrwheninvokingclosethinkagain
*/
if (errno == EINTR)
return 0;
return -errno;
}
int safe_close(int fd) {
/*
* Like close_nointr() but cannot fail. Guarantees errno is
* unchanged. Is a NOP with negative fds passed, and returns
* -1, so that it can be used in this syntax:
*
* fd = safe_close(fd);
*/
if (fd >= 0) {
PROTECT_ERRNO;
/* The kernel might return pretty much any error code
* via close(), but the fd will be closed anyway. The
* only condition we want to check for here is whether
* the fd was invalid at all... */
assert_se(close_nointr(fd) != -EBADF);
}
return -1;
}
void safe_close_pair(int p[static 2]) {
assert(p);
if (p[0] == p[1]) {
/* Special case pairs which use the same fd in both
* directions... */
p[0] = p[1] = safe_close(p[0]);
return;
}
p[0] = safe_close(p[0]);
p[1] = safe_close(p[1]);
}
void close_many(const int fds[], size_t n_fd) {
size_t i;
assert(fds || n_fd <= 0);
for (i = 0; i < n_fd; i++)
safe_close(fds[i]);
}
int fclose_nointr(FILE *f) {
assert(f);
/* Same as close_nointr(), but for fclose() */
errno = 0; /* Extra safety: if the FILE* object is not encapsulating an fd, it might not set errno
* correctly. Let's hence initialize it to zero first, so that we aren't confused by any
* prior errno here */
if (fclose(f) == 0)
return 0;
if (errno == EINTR)
return 0;
return errno_or_else(EIO);
}
FILE* safe_fclose(FILE *f) {
/* Same as safe_close(), but for fclose() */
if (f) {
PROTECT_ERRNO;
assert_se(fclose_nointr(f) != -EBADF);
}
return NULL;
}
DIR* safe_closedir(DIR *d) {
if (d) {
PROTECT_ERRNO;
assert_se(closedir(d) >= 0 || errno != EBADF);
}
return NULL;
}
int fd_nonblock(int fd, bool nonblock) {
int flags, nflags;
assert(fd >= 0);
flags = fcntl(fd, F_GETFL, 0);
if (flags < 0)
return -errno;
nflags = UPDATE_FLAG(flags, O_NONBLOCK, nonblock);
if (nflags == flags)
return 0;
if (fcntl(fd, F_SETFL, nflags) < 0)
return -errno;
return 0;
}
int fd_cloexec(int fd, bool cloexec) {
int flags, nflags;
assert(fd >= 0);
flags = fcntl(fd, F_GETFD, 0);
if (flags < 0)
return -errno;
nflags = UPDATE_FLAG(flags, FD_CLOEXEC, cloexec);
if (nflags == flags)
return 0;
if (fcntl(fd, F_SETFD, nflags) < 0)
return -errno;
return 0;
}
#if 0 /* NM_IGNORED */
_pure_ static bool fd_in_set(int fd, const int fdset[], size_t n_fdset) {
size_t i;
assert(n_fdset == 0 || fdset);
for (i = 0; i < n_fdset; i++)
if (fdset[i] == fd)
return true;
return false;
}
static int get_max_fd(void) {
struct rlimit rl;
rlim_t m;
/* Return the highest possible fd, based RLIMIT_NOFILE, but enforcing FD_SETSIZE-1 as lower boundary
* and INT_MAX as upper boundary. */
if (getrlimit(RLIMIT_NOFILE, &rl) < 0)
return -errno;
m = MAX(rl.rlim_cur, rl.rlim_max);
if (m < FD_SETSIZE) /* Let's always cover at least 1024 fds */
return FD_SETSIZE-1;
if (m == RLIM_INFINITY || m > INT_MAX) /* Saturate on overflow. After all fds are "int", hence can
* never be above INT_MAX */
return INT_MAX;
return (int) (m - 1);
}
int close_all_fds(const int except[], size_t n_except) {
static bool have_close_range = true; /* Assume we live in the future */
_cleanup_closedir_ DIR *d = NULL;
struct dirent *de;
int r = 0;
assert(n_except == 0 || except);
if (have_close_range) {
/* In the best case we have close_range() to close all fds between a start and an end fd,
* which we can use on the "inverted" exception array, i.e. all intervals between all
* adjacent pairs from the sorted exception array. This changes loop complexity from O(n)
* where n is number of open fds to O(m⋅log(m)) where m is the number of fds to keep
* open. Given that we assume n ≫ m that's preferable to us. */
if (n_except == 0) {
/* Close everything. Yay! */
if (close_range(3, -1, 0) >= 0)
return 1;
if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
return -errno;
have_close_range = false;
} else {
_cleanup_free_ int *sorted_malloc = NULL;
size_t n_sorted;
int *sorted;
assert(n_except < SIZE_MAX);
n_sorted = n_except + 1;
if (n_sorted > 64) /* Use heap for large numbers of fds, stack otherwise */
sorted = sorted_malloc = new(int, n_sorted);
else
sorted = newa(int, n_sorted);
if (sorted) {
int c = 0;
memcpy(sorted, except, n_except * sizeof(int));
/* Let's add fd 2 to the list of fds, to simplify the loop below, as this
* allows us to cover the head of the array the same way as the body */
sorted[n_sorted-1] = 2;
typesafe_qsort(sorted, n_sorted, cmp_int);
for (size_t i = 0; i < n_sorted-1; i++) {
int start, end;
start = MAX(sorted[i], 2); /* The first three fds shall always remain open */
end = MAX(sorted[i+1], 2);
assert(end >= start);
if (end - start <= 1)
continue;
/* Close everything between the start and end fds (both of which shall stay open) */
if (close_range(start + 1, end - 1, 0) < 0) {
if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
return -errno;
have_close_range = false;
break;
}
c += end - start - 1;
}
if (have_close_range) {
/* The loop succeeded. Let's now close everything beyond the end */
if (sorted[n_sorted-1] >= INT_MAX) /* Dont let the addition below overflow */
return c;
if (close_range(sorted[n_sorted-1] + 1, -1, 0) >= 0)
return c + 1;
if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
return -errno;
have_close_range = false;
}
}
}
/* Fallback on OOM or if close_range() is not supported */
}
d = opendir("/proc/self/fd");
if (!d) {
int fd, max_fd;
/* When /proc isn't available (for example in chroots) the fallback is brute forcing through
* the fd table */
max_fd = get_max_fd();
if (max_fd < 0)
return max_fd;
/* Refuse to do the loop over more too many elements. It's better to fail immediately than to
* spin the CPU for a long time. */
if (max_fd > MAX_FD_LOOP_LIMIT)
return log_debug_errno(SYNTHETIC_ERRNO(EPERM),
"/proc/self/fd is inaccessible. Refusing to loop over %d potential fds.",
max_fd);
for (fd = 3; fd >= 0; fd = fd < max_fd ? fd + 1 : -1) {
int q;
if (fd_in_set(fd, except, n_except))
continue;
q = close_nointr(fd);
if (q < 0 && q != -EBADF && r >= 0)
r = q;
}
return r;
}
FOREACH_DIRENT(de, d, return -errno) {
int fd = -1, q;
if (safe_atoi(de->d_name, &fd) < 0)
/* Let's better ignore this, just in case */
continue;
if (fd < 3)
continue;
if (fd == dirfd(d))
continue;
if (fd_in_set(fd, except, n_except))
continue;
q = close_nointr(fd);
if (q < 0 && q != -EBADF && r >= 0) /* Valgrind has its own FD and doesn't want to have it closed */
r = q;
}
return r;
}
int same_fd(int a, int b) {
struct stat sta, stb;
pid_t pid;
int r, fa, fb;
assert(a >= 0);
assert(b >= 0);
/* Compares two file descriptors. Note that semantics are
* quite different depending on whether we have kcmp() or we
* don't. If we have kcmp() this will only return true for
* dup()ed file descriptors, but not otherwise. If we don't
* have kcmp() this will also return true for two fds of the same
* file, created by separate open() calls. Since we use this
* call mostly for filtering out duplicates in the fd store
* this difference hopefully doesn't matter too much. */
if (a == b)
return true;
/* Try to use kcmp() if we have it. */
pid = getpid_cached();
r = kcmp(pid, pid, KCMP_FILE, a, b);
if (r == 0)
return true;
if (r > 0)
return false;
if (!IN_SET(errno, ENOSYS, EACCES, EPERM))
return -errno;
/* We don't have kcmp(), use fstat() instead. */
if (fstat(a, &sta) < 0)
return -errno;
if (fstat(b, &stb) < 0)
return -errno;
if ((sta.st_mode & S_IFMT) != (stb.st_mode & S_IFMT))
return false;
/* We consider all device fds different, since two device fds
* might refer to quite different device contexts even though
* they share the same inode and backing dev_t. */
if (S_ISCHR(sta.st_mode) || S_ISBLK(sta.st_mode))
return false;
if (sta.st_dev != stb.st_dev || sta.st_ino != stb.st_ino)
return false;
/* The fds refer to the same inode on disk, let's also check
* if they have the same fd flags. This is useful to
* distinguish the read and write side of a pipe created with
* pipe(). */
fa = fcntl(a, F_GETFL);
if (fa < 0)
return -errno;
fb = fcntl(b, F_GETFL);
if (fb < 0)
return -errno;
return fa == fb;
}
#endif /* NM_IGNORED */
void cmsg_close_all(struct msghdr *mh) {
struct cmsghdr *cmsg;
assert(mh);
CMSG_FOREACH(cmsg, mh)
if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS)
close_many((int*) CMSG_DATA(cmsg), (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int));
}
bool fdname_is_valid(const char *s) {
const char *p;
/* Validates a name for $LISTEN_FDNAMES. We basically allow
* everything ASCII that's not a control character. Also, as
* special exception the ":" character is not allowed, as we
* use that as field separator in $LISTEN_FDNAMES.
*
* Note that the empty string is explicitly allowed
* here. However, we limit the length of the names to 255
* characters. */
if (!s)
return false;
for (p = s; *p; p++) {
if (*p < ' ')
return false;
if (*p >= 127)
return false;
if (*p == ':')
return false;
}
return p - s < 256;
}
#if 0 /* NM_IGNORED */
int fd_get_path(int fd, char **ret) {
char procfs_path[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int)];
int r;
xsprintf(procfs_path, "/proc/self/fd/%i", fd);
r = readlink_malloc(procfs_path, ret);
if (r == -ENOENT) {
/* ENOENT can mean two things: that the fd does not exist or that /proc is not mounted. Let's make
* things debuggable and distinguish the two. */
if (proc_mounted() == 0)
return -ENOSYS; /* /proc is not available or not set up properly, we're most likely in some chroot
* environment. */
return -EBADF; /* The directory exists, hence it's the fd that doesn't. */
}
return r;
}
int move_fd(int from, int to, int cloexec) {
int r;
/* Move fd 'from' to 'to', make sure FD_CLOEXEC remains equal if requested, and release the old fd. If
* 'cloexec' is passed as -1, the original FD_CLOEXEC is inherited for the new fd. If it is 0, it is turned
* off, if it is > 0 it is turned on. */
if (from < 0)
return -EBADF;
if (to < 0)
return -EBADF;
if (from == to) {
if (cloexec >= 0) {
r = fd_cloexec(to, cloexec);
if (r < 0)
return r;
}
return to;
}
if (cloexec < 0) {
int fl;
fl = fcntl(from, F_GETFD, 0);
if (fl < 0)
return -errno;
cloexec = !!(fl & FD_CLOEXEC);
}
r = dup3(from, to, cloexec ? O_CLOEXEC : 0);
if (r < 0)
return -errno;
assert(r == to);
safe_close(from);
return to;
}
int acquire_data_fd(const void *data, size_t size, unsigned flags) {
_cleanup_close_pair_ int pipefds[2] = { -1, -1 };
char pattern[] = "/dev/shm/data-fd-XXXXXX";
_cleanup_close_ int fd = -1;
int isz = 0, r;
ssize_t n;
off_t f;
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 */
r = open("/dev/null", O_RDONLY|O_CLOEXEC|O_NOCTTY);
if (r < 0)
return -errno;
return r;
}
if ((flags & ACQUIRE_NO_MEMFD) == 0) {
fd = memfd_new("data-fd");
if (fd < 0)
goto try_pipe;
n = write(fd, data, size);
if (n < 0)
return -errno;
if ((size_t) n != size)
return -EIO;
f = lseek(fd, 0, SEEK_SET);
if (f != 0)
return -errno;
r = memfd_set_sealed(fd);
if (r < 0)
return r;
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) {
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 = open(pattern, O_RDONLY|O_CLOEXEC);
if (r < 0)
r = -errno;
unlink_and_return:
(void) unlink(pattern);
return r;
}
return -EOPNOTSUPP;
}
/* 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 fd_duplicate_data_fd(int fd) {
_cleanup_close_ int copy_fd = -1, tmp_fd = -1;
_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_pairp) int pipefds[2] = { -1, -1 };
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, false);
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, false);
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);
}
#endif /* NM_IGNORED */
int fd_move_above_stdio(int fd) {
int flags, copy;
PROTECT_ERRNO;
/* Moves the specified file descriptor if possible out of the range [0…2], i.e. the range of
* stdin/stdout/stderr. If it can't be moved outside of this range the original file descriptor is
* returned. This call is supposed to be used for long-lasting file descriptors we allocate in our code that
* might get loaded into foreign code, and where we want ensure our fds are unlikely used accidentally as
* stdin/stdout/stderr of unrelated code.
*
* Note that this doesn't fix any real bugs, it just makes it less likely that our code will be affected by
* buggy code from others that mindlessly invokes 'fprintf(stderr, …' or similar in places where stderr has
* been closed before.
*
* This function is written in a "best-effort" and "least-impact" style. This means whenever we encounter an
* error we simply return the original file descriptor, and we do not touch errno. */
if (fd < 0 || fd > 2)
return fd;
flags = fcntl(fd, F_GETFD, 0);
if (flags < 0)
return fd;
if (flags & FD_CLOEXEC)
copy = fcntl(fd, F_DUPFD_CLOEXEC, 3);
else
copy = fcntl(fd, F_DUPFD, 3);
if (copy < 0)
return fd;
assert(copy > 2);
(void) close(fd);
return copy;
}
#if 0 /* NM_IGNORED */
int rearrange_stdio(int original_input_fd, int original_output_fd, int original_error_fd) {
int fd[3] = { /* Put together an array of fds we work on */
original_input_fd,
original_output_fd,
original_error_fd
};
int r, i,
null_fd = -1, /* if we open /dev/null, we store the fd to it here */
copy_fd[3] = { -1, -1, -1 }; /* This contains all fds we duplicate here temporarily, and hence need to close at the end */
bool null_readable, null_writable;
/* Sets up stdin, stdout, stderr with the three file descriptors passed in. If any of the descriptors is
* specified as -1 it will be connected with /dev/null instead. If any of the file descriptors is passed as
* itself (e.g. stdin as STDIN_FILENO) it is left unmodified, but the O_CLOEXEC bit is turned off should it be
* on.
*
* Note that if any of the passed file descriptors are > 2 they will be closed — both on success and on
* failure! Thus, callers should assume that when this function returns the input fds are invalidated.
*
* Note that when this function fails stdin/stdout/stderr might remain half set up!
*
* O_CLOEXEC is turned off for all three file descriptors (which is how it should be for
* stdin/stdout/stderr). */
null_readable = original_input_fd < 0;
null_writable = original_output_fd < 0 || original_error_fd < 0;
/* First step, open /dev/null once, if we need it */
if (null_readable || null_writable) {
/* Let's open this with O_CLOEXEC first, and convert it to non-O_CLOEXEC when we move the fd to the final position. */
null_fd = open("/dev/null", (null_readable && null_writable ? O_RDWR :
null_readable ? O_RDONLY : O_WRONLY) | O_CLOEXEC);
if (null_fd < 0) {
r = -errno;
goto finish;
}
/* If this fd is in the 0…2 range, let's move it out of it */
if (null_fd < 3) {
int copy;
copy = fcntl(null_fd, F_DUPFD_CLOEXEC, 3); /* Duplicate this with O_CLOEXEC set */
if (copy < 0) {
r = -errno;
goto finish;
}
CLOSE_AND_REPLACE(null_fd, copy);
}
}
/* Let's assemble fd[] with the fds to install in place of stdin/stdout/stderr */
for (i = 0; i < 3; i++) {
if (fd[i] < 0)
fd[i] = null_fd; /* A negative parameter means: connect this one to /dev/null */
else if (fd[i] != i && fd[i] < 3) {
/* This fd is in the 0…2 territory, but not at its intended place, move it out of there, so that we can work there. */
copy_fd[i] = fcntl(fd[i], F_DUPFD_CLOEXEC, 3); /* Duplicate this with O_CLOEXEC set */
if (copy_fd[i] < 0) {
r = -errno;
goto finish;
}
fd[i] = copy_fd[i];
}
}
/* At this point we now have the fds to use in fd[], and they are all above the stdio range, so that we
* have freedom to move them around. If the fds already were at the right places then the specific fds are
* -1. Let's now move them to the right places. This is the point of no return. */
for (i = 0; i < 3; i++) {
if (fd[i] == i) {
/* fd is already in place, but let's make sure O_CLOEXEC is off */
r = fd_cloexec(i, false);
if (r < 0)
goto finish;
} else {
assert(fd[i] > 2);
if (dup2(fd[i], i) < 0) { /* Turns off O_CLOEXEC on the new fd. */
r = -errno;
goto finish;
}
}
}
r = 0;
finish:
/* Close the original fds, but only if they were outside of the stdio range. Also, properly check for the same
* fd passed in multiple times. */
safe_close_above_stdio(original_input_fd);
if (original_output_fd != original_input_fd)
safe_close_above_stdio(original_output_fd);
if (original_error_fd != original_input_fd && original_error_fd != original_output_fd)
safe_close_above_stdio(original_error_fd);
/* Close the copies we moved > 2 */
for (i = 0; i < 3; i++)
safe_close(copy_fd[i]);
/* Close our null fd, if it's > 2 */
safe_close_above_stdio(null_fd);
return r;
}
int fd_reopen(int fd, int flags) {
char procfs_path[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int)];
int new_fd;
/* Reopens the specified fd with new flags. This is useful for convert an O_PATH fd into a regular one, or to
* turn O_RDWR fds into O_RDONLY fds.
*
* This doesn't work on sockets (since they cannot be open()ed, ever).
*
* This implicitly resets the file read index to 0. */
xsprintf(procfs_path, "/proc/self/fd/%i", fd);
new_fd = open(procfs_path, flags);
if (new_fd < 0) {
if (errno != ENOENT)
return -errno;
if (proc_mounted() == 0)
return -ENOSYS; /* if we have no /proc/, the concept is not implementable */
return -ENOENT;
}
return new_fd;
}
int read_nr_open(void) {
_cleanup_free_ char *nr_open = NULL;
int r;
/* Returns the kernel's current fd limit, either by reading it of /proc/sys if that works, or using the
* hard-coded default compiled-in value of current kernels (1M) if not. This call will never fail. */
r = read_one_line_file("/proc/sys/fs/nr_open", &nr_open);
if (r < 0)
log_debug_errno(r, "Failed to read /proc/sys/fs/nr_open, ignoring: %m");
else {
int v;
r = safe_atoi(nr_open, &v);
if (r < 0)
log_debug_errno(r, "Failed to parse /proc/sys/fs/nr_open value '%s', ignoring: %m", nr_open);
else
return v;
}
/* If we fail, fall back to the hard-coded kernel limit of 1024 * 1024. */
return 1024 * 1024;
}
#endif /* NM_IGNORED */