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systemd/src/basic/fd-util.c

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <errno.h>
#include <fcntl.h>
#if WANT_LINUX_FS_H
#include <linux/fs.h>
#endif
#include <linux/magic.h>
#include <sys/ioctl.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <unistd.h>
#include "alloc-util.h"
#include "dirent-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "fs-util.h"
#include "io-util.h"
#include "macro.h"
#include "missing_fcntl.h"
#include "missing_fs.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"
/* 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 noop for negative fds,
* and returns -EBADF, 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 -EBADF;
}
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) {
assert(fds || n_fd <= 0);
for (size_t 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;
return RET_NERRNO(fcntl(fd, F_SETFL, nflags));
}
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;
return RET_NERRNO(fcntl(fd, F_SETFD, nflags));
}
int fd_cloexec_many(const int fds[], size_t n_fds, bool cloexec) {
int ret = 0, r;
assert(n_fds == 0 || fds);
for (size_t i = 0; i < n_fds; i++) {
if (fds[i] < 0) /* Skip gracefully over already invalidated fds */
continue;
r = fd_cloexec(fds[i], cloexec);
if (r < 0 && ret >= 0) /* Continue going, but return first error */
ret = r;
else
ret = 1; /* report if we did anything */
}
return ret;
}
_pure_ static bool fd_in_set(int fd, const int fdset[], size_t n_fdset) {
assert(n_fdset == 0 || fdset);
for (size_t i = 0; i < n_fdset; i++) {
if (fdset[i] < 0)
continue;
if (fdset[i] == fd)
return true;
}
return false;
}
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);
}
static int close_all_fds_frugal(const int except[], size_t n_except) {
int max_fd, r = 0;
assert(n_except == 0 || except);
/* This is the inner fallback core of close_all_fds(). This never calls malloc() or opendir() or so
* and hence is safe to be called in signal handler context. Most users should call close_all_fds(),
* but when we assume we are called from signal handler context, then use this simpler call
* instead. */
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),
"Refusing to loop over %d potential fds.",
max_fd);
for (int fd = 3; fd >= 0; fd = fd < max_fd ? fd + 1 : -EBADF) {
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;
}
static bool have_close_range = true; /* Assume we live in the future */
static int close_all_fds_special_case(const int except[], size_t n_except) {
assert(n_except == 0 || except);
/* Handles a few common special cases separately, since they are common and can be optimized really
* nicely, since we won't need sorting for them. Returns > 0 if the special casing worked, 0
* otherwise. */
if (!have_close_range)
return 0;
if (n_except == 1 && except[0] < 0) /* Minor optimization: if we only got one fd, and it's invalid,
* we got none */
n_except = 0;
switch (n_except) {
case 0:
/* Close everything. Yay! */
if (close_range(3, -1, 0) >= 0)
return 1;
if (ERRNO_IS_NOT_SUPPORTED(errno) || ERRNO_IS_PRIVILEGE(errno)) {
have_close_range = false;
return 0;
}
return -errno;
case 1:
/* Close all but exactly one, then we don't need no sorting. This is a pretty common
* case, hence let's handle it specially. */
if ((except[0] <= 3 || close_range(3, except[0]-1, 0) >= 0) &&
(except[0] >= INT_MAX || close_range(MAX(3, except[0]+1), -1, 0) >= 0))
return 1;
if (ERRNO_IS_NOT_SUPPORTED(errno) || ERRNO_IS_PRIVILEGE(errno)) {
have_close_range = false;
return 0;
}
return -errno;
default:
return 0;
}
}
int close_all_fds_without_malloc(const int except[], size_t n_except) {
int r;
assert(n_except == 0 || except);
r = close_all_fds_special_case(except, n_except);
if (r < 0)
return r;
if (r > 0) /* special case worked! */
return 0;
return close_all_fds_frugal(except, n_except);
}
int close_all_fds(const int except[], size_t n_except) {
_cleanup_closedir_ DIR *d = NULL;
int r = 0;
assert(n_except == 0 || except);
r = close_all_fds_special_case(except, n_except);
if (r < 0)
return r;
if (r > 0) /* special case worked! */
return 0;
if (have_close_range) {
_cleanup_free_ int *sorted_malloc = NULL;
size_t n_sorted;
int *sorted;
/* 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. */
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) {
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;
}
}
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 0;
if (close_range(sorted[n_sorted-1] + 1, -1, 0) >= 0)
return 0;
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)
return close_all_fds_frugal(except, n_except); /* ultimate fallback if /proc/ is not available */
FOREACH_DIRENT(de, d, return -errno) {
int fd = -EBADF, q;
if (!IN_SET(de->d_type, DT_LNK, DT_UNKNOWN))
continue;
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 (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
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 (!stat_inode_same(&sta, &stb))
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;
/* 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;
}
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(CMSG_TYPED_DATA(cmsg, int),
(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 <= FDNAME_MAX;
}
int fd_get_path(int fd, char **ret) {
int r;
r = readlink_malloc(FORMAT_PROC_FD_PATH(fd), 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 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;
}
int rearrange_stdio(int original_input_fd, int original_output_fd, int original_error_fd) {
int fd[3] = { original_input_fd, /* Put together an array of fds we work on */
original_output_fd,
original_error_fd },
null_fd = -EBADF, /* If we open /dev/null, we store the fd to it here */
copy_fd[3] = { -EBADF, -EBADF, -EBADF }, /* This contains all fds we duplicate here
* temporarily, and hence need to close at the end. */
r;
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 -EBADF 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 (int 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 -EBADF. Let's now move them to the right places. This is the point of no return. */
for (int 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 (int 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) {
int new_fd, r;
/* 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. */
if (FLAGS_SET(flags, O_DIRECTORY)) {
/* If we shall reopen the fd as directory we can just go via "." and thus bypass the whole
* magic /proc/ directory, and make ourselves independent of that being mounted. */
new_fd = openat(fd, ".", flags);
if (new_fd < 0)
return -errno;
return new_fd;
}
new_fd = open(FORMAT_PROC_FD_PATH(fd), flags);
if (new_fd < 0) {
if (errno != ENOENT)
return -errno;
r = proc_mounted();
if (r == 0)
return -ENOSYS; /* if we have no /proc/, the concept is not implementable */
return r > 0 ? -EBADF : -ENOENT; /* If /proc/ is definitely around then this means the fd is
* not valid, otherwise let's propagate the original
* error */
}
return new_fd;
}
int fd_reopen_condition(
int fd,
int flags,
int mask,
int *ret_new_fd) {
int r, new_fd;
assert(fd >= 0);
/* Invokes fd_reopen(fd, flags), but only if the existing F_GETFL flags don't match the specified
* flags (masked by the specified mask). This is useful for converting O_PATH fds into real fds if
* needed, but only then. */
r = fcntl(fd, F_GETFL);
if (r < 0)
return -errno;
if ((r & mask) == (flags & mask)) {
*ret_new_fd = -EBADF;
return fd;
}
new_fd = fd_reopen(fd, flags);
if (new_fd < 0)
return new_fd;
*ret_new_fd = new_fd;
return new_fd;
}
int fd_is_opath(int fd) {
int r;
assert(fd >= 0);
r = fcntl(fd, F_GETFL);
if (r < 0)
return -errno;
return FLAGS_SET(r, O_PATH);
}
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;
}
int fd_get_diskseq(int fd, uint64_t *ret) {
uint64_t diskseq;
assert(fd >= 0);
assert(ret);
if (ioctl(fd, BLKGETDISKSEQ, &diskseq) < 0) {
/* Note that the kernel is weird: non-existing ioctls currently return EINVAL
* rather than ENOTTY on loopback block devices. They should fix that in the kernel,
* but in the meantime we accept both here. */
if (!ERRNO_IS_NOT_SUPPORTED(errno) && errno != EINVAL)
return -errno;
return -EOPNOTSUPP;
}
*ret = diskseq;
return 0;
}
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