/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include #include #include #include #include #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; } _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); } static int cmp_int(const int *a, const int *b) { return CMP(*a, *b); } 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; } 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; } 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/. 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); } 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] = { /* 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; }