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053fe27343
The __closefrom_fallback tries to get a available file descriptor
if the initial open ("/proc/self/fd/", ...) fails. It assumes the
failure would be only if procfs is not mount (ENOENT), however if
the the proc file is not accessible (due some other kernel filtering
such apparmor) it will iterate over a potentially large file set
issuing close calls.
It should only try the close fallback if open returns EMFILE,
ENFILE, or ENOMEM.
Checked on x86_64-linux-gnu.
105 lines
3.3 KiB
C
105 lines
3.3 KiB
C
/* Close a range of file descriptors. Linux version.
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Copyright (C) 2021-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <arch-fd_to_filename.h>
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#include <dirent.h>
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#include <not-cancel.h>
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#include <stdbool.h>
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#if !__ASSUME_CLOSE_RANGE
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/* Fallback code: iterates over /proc/self/fd, closing each file descriptor
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that fall on the criteria. If DIRFD_FALLBACK is set, a failure on
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/proc/self/fd open will trigger a fallback that tries to close a file
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descriptor before proceed. */
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_Bool
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__closefrom_fallback (int from, _Bool dirfd_fallback)
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{
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int dirfd = __open_nocancel (FD_TO_FILENAME_PREFIX, O_RDONLY | O_DIRECTORY,
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0);
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if (dirfd == -1)
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{
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/* Return if procfs can not be opened for some reason. */
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if ((errno != EMFILE && errno != ENFILE && errno != ENOMEM)
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|| !dirfd_fallback)
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return false;
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/* The closefrom should work even when process can't open new files. */
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for (int i = from; i < INT_MAX; i++)
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{
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int r = __close_nocancel (i);
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if (r == 0 || (r == -1 && errno != EBADF))
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break;
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}
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dirfd = __open_nocancel (FD_TO_FILENAME_PREFIX, O_RDONLY | O_DIRECTORY,
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0);
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if (dirfd == -1)
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return false;
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}
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char buffer[1024];
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bool ret = false;
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while (true)
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{
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ssize_t ret = __getdents64 (dirfd, buffer, sizeof (buffer));
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if (ret == -1)
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goto err;
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else if (ret == 0)
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break;
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/* If any file descriptor is closed it resets the /proc/self position
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read again from the start (to obtain any possible kernel update). */
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bool closed = false;
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char *begin = buffer, *end = buffer + ret;
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while (begin != end)
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{
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unsigned short int d_reclen;
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memcpy (&d_reclen, begin + offsetof (struct dirent64, d_reclen),
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sizeof (d_reclen));
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const char *dname = begin + offsetof (struct dirent64, d_name);
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begin += d_reclen;
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if (dname[0] == '.')
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continue;
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int fd = 0;
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for (const char *s = dname; (unsigned int) (*s) - '0' < 10; s++)
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fd = 10 * fd + (*s - '0');
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if (fd == dirfd || fd < from)
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continue;
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/* We ignore close errors because EBADF, EINTR, and EIO means the
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descriptor has been released. */
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__close_nocancel (fd);
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closed = true;
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}
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if (closed && __lseek (dirfd, 0, SEEK_SET) < 0)
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goto err;
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}
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ret = true;
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err:
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__close_nocancel (dirfd);
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return ret;
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}
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#endif
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