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111 lines
3.7 KiB
C
111 lines
3.7 KiB
C
/* Create /proc/self/fd-related names for subfiles of open directories.
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Copyright (C) 2006, 2009-2014 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program 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
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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/* Written by Paul Eggert. */
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#include <config.h>
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#include "openat-priv.h"
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include "intprops.h"
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/* The results of open() in this file are not used with fchdir,
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and we do not leak fds to any single-threaded code that could use stdio,
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therefore save some unnecessary work in fchdir.c.
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FIXME - if the kernel ever adds support for multi-thread safety for
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avoiding standard fds, then we should use open_safer. */
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#undef open
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#undef close
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#define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/%s"
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#define PROC_SELF_FD_NAME_SIZE_BOUND(len) \
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(sizeof PROC_SELF_FD_FORMAT - sizeof "%d%s" \
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+ INT_STRLEN_BOUND (int) + (len) + 1)
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/* Set BUF to the expansion of PROC_SELF_FD_FORMAT, using FD and FILE
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respectively for %d and %s. If successful, return BUF if the
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result fits in BUF, dynamically allocated memory otherwise. But
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return NULL if /proc is not reliable, either because the operating
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system support is lacking or because memory is low. */
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char *
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openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file)
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{
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static int proc_status = 0;
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/* Make sure the caller gets ENOENT when appropriate. */
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if (!*file)
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{
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buf[0] = '\0';
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return buf;
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}
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if (! proc_status)
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{
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/* Set PROC_STATUS to a positive value if /proc/self/fd is
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reliable, and a negative value otherwise. Solaris 10
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/proc/self/fd mishandles "..", and any file name might expand
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to ".." after symbolic link expansion, so avoid /proc/self/fd
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if it mishandles "..". Solaris 10 has openat, but this
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problem is exhibited on code that built on Solaris 8 and
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running on Solaris 10. */
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int proc_self_fd = open ("/proc/self/fd",
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O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
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if (proc_self_fd < 0)
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proc_status = -1;
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else
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{
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/* Detect whether /proc/self/fd/%i/../fd exists, where %i is the
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number of a file descriptor open on /proc/self/fd. On Linux,
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that name resolves to /proc/self/fd, which was opened above.
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However, on Solaris, it may resolve to /proc/self/fd/fd, which
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cannot exist, since all names in /proc/self/fd are numeric. */
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char dotdot_buf[PROC_SELF_FD_NAME_SIZE_BOUND (sizeof "../fd" - 1)];
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sprintf (dotdot_buf, PROC_SELF_FD_FORMAT, proc_self_fd, "../fd");
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proc_status = access (dotdot_buf, F_OK) ? -1 : 1;
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close (proc_self_fd);
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}
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}
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if (proc_status < 0)
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return NULL;
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else
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{
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size_t bufsize = PROC_SELF_FD_NAME_SIZE_BOUND (strlen (file));
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char *result = buf;
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if (OPENAT_BUFFER_SIZE < bufsize)
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{
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result = malloc (bufsize);
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if (! result)
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return NULL;
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}
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sprintf (result, PROC_SELF_FD_FORMAT, fd, file);
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return result;
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}
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}
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