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/* Define 2-FD at-style functions like linkat or renameat.
Copyright (C) 2006, 2009-2023 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* written by Jim Meyering and Eric Blake */
#include <config.h>
#include "openat-priv.h"
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "filename.h" /* solely for definition of IS_ABSOLUTE_FILE_NAME */
#include "filenamecat.h"
#include "openat.h"
#include "same-inode.h"
#include "save-cwd.h"
/* Call FUNC to operate on a pair of files, where FILE1 is relative to FD1,
and FILE2 is relative to FD2. If possible, do it without changing the
working directory. Otherwise, resort to using save_cwd/fchdir,
FUNC, restore_cwd (up to two times). If either the save_cwd or the
restore_cwd fails, then give a diagnostic and exit nonzero. */
int
at_func2 (int fd1, char const *file1,
int fd2, char const *file2,
int (*func) (char const *file1, char const *file2))
{
struct saved_cwd saved_cwd;
int saved_errno;
int err;
char *file1_alt;
char *file2_alt;
struct stat st1;
struct stat st2;
/* There are 16 possible scenarios, based on whether an fd is
AT_FDCWD or real, and whether a file is absolute or relative:
fd1 file1 fd2 file2 action
0 cwd abs cwd abs direct call
1 cwd abs cwd rel direct call
2 cwd abs fd abs direct call
3 cwd abs fd rel chdir to fd2
4 cwd rel cwd abs direct call
5 cwd rel cwd rel direct call
6 cwd rel fd abs direct call
7 cwd rel fd rel convert file1 to abs, then case 3
8 fd abs cwd abs direct call
9 fd abs cwd rel direct call
10 fd abs fd abs direct call
11 fd abs fd rel chdir to fd2
12 fd rel cwd abs chdir to fd1
13 fd rel cwd rel convert file2 to abs, then case 12
14 fd rel fd abs chdir to fd1
15a fd1 rel fd1 rel chdir to fd1
15b fd1 rel fd2 rel chdir to fd1, then case 7
Try some optimizations to reduce fd to AT_FDCWD, or to at least
avoid converting an absolute name or doing a double chdir. */
if ((fd1 == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file1))
&& (fd2 == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file2)))
return func (file1, file2); /* Case 0-2, 4-6, 8-10. */
/* If /proc/self/fd works, we don't need any stat or chdir. */
{
char proc_buf1[OPENAT_BUFFER_SIZE];
char *proc_file1 = ((fd1 == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file1))
? (char *) file1
: openat_proc_name (proc_buf1, fd1, file1));
if (proc_file1)
{
char proc_buf2[OPENAT_BUFFER_SIZE];
char *proc_file2 = ((fd2 == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file2))
? (char *) file2
: openat_proc_name (proc_buf2, fd2, file2));
if (proc_file2)
{
int proc_result = func (proc_file1, proc_file2);
int proc_errno = errno;
if (proc_file1 != proc_buf1 && proc_file1 != file1)
free (proc_file1);
if (proc_file2 != proc_buf2 && proc_file2 != file2)
free (proc_file2);
/* If the syscall succeeds, or if it fails with an unexpected
errno value, then return right away. Otherwise, fall through
and resort to using save_cwd/restore_cwd. */
if (0 <= proc_result)
return proc_result;
if (! EXPECTED_ERRNO (proc_errno))
{
errno = proc_errno;
return proc_result;
}
}
else if (proc_file1 != proc_buf1 && proc_file1 != file1)
free (proc_file1);
}
}
/* Cases 3, 7, 11-15 remain. Time to normalize directory fds, if
possible. */
if (IS_ABSOLUTE_FILE_NAME (file1))
fd1 = AT_FDCWD; /* Case 11 reduced to 3. */
else if (IS_ABSOLUTE_FILE_NAME (file2))
fd2 = AT_FDCWD; /* Case 14 reduced to 12. */
/* Cases 3, 7, 12, 13, 15 remain. */
if (fd1 == AT_FDCWD) /* Cases 3, 7. */
{
if (stat (".", &st1) == -1 || fstat (fd2, &st2) == -1)
return -1;
if (!S_ISDIR (st2.st_mode))
{
errno = ENOTDIR;
return -1;
}
if (SAME_INODE (st1, st2)) /* Reduced to cases 1, 5. */
return func (file1, file2);
}
else if (fd2 == AT_FDCWD) /* Cases 12, 13. */
{
if (stat (".", &st2) == -1 || fstat (fd1, &st1) == -1)
return -1;
if (!S_ISDIR (st1.st_mode))
{
errno = ENOTDIR;
return -1;
}
if (SAME_INODE (st1, st2)) /* Reduced to cases 4, 5. */
return func (file1, file2);
}
else if (fd1 != fd2) /* Case 15b. */
{
if (fstat (fd1, &st1) == -1 || fstat (fd2, &st2) == -1)
return -1;
if (!S_ISDIR (st1.st_mode) || !S_ISDIR (st2.st_mode))
{
errno = ENOTDIR;
return -1;
}
if (SAME_INODE (st1, st2)) /* Reduced to case 15a. */
{
fd2 = fd1;
if (stat (".", &st1) == 0 && SAME_INODE (st1, st2))
return func (file1, file2); /* Further reduced to case 5. */
}
}
else /* Case 15a. */
{
if (fstat (fd1, &st1) == -1)
return -1;
if (!S_ISDIR (st1.st_mode))
{
errno = ENOTDIR;
return -1;
}
if (stat (".", &st2) == 0 && SAME_INODE (st1, st2))
return func (file1, file2); /* Reduced to case 5. */
}
/* Catch invalid arguments before changing directories. */
if (file1[0] == '\0' || file2[0] == '\0')
{
errno = ENOENT;
return -1;
}
/* Cases 3, 7, 12, 13, 15a, 15b remain. With all reductions in
place, it is time to start changing directories. */
if (save_cwd (&saved_cwd) != 0)
openat_save_fail (errno);
if (fd1 != AT_FDCWD && fd2 != AT_FDCWD && fd1 != fd2) /* Case 15b. */
{
if (fchdir (fd1) != 0)
{
saved_errno = errno;
free_cwd (&saved_cwd);
errno = saved_errno;
return -1;
}
fd1 = AT_FDCWD; /* Reduced to case 7. */
}
/* Cases 3, 7, 12, 13, 15a remain. Convert one relative name to
absolute, if necessary. */
file1_alt = (char *) file1;
file2_alt = (char *) file2;
if (fd1 == AT_FDCWD && !IS_ABSOLUTE_FILE_NAME (file1)) /* Case 7. */
{
/* It would be nicer to use:
file1_alt = file_name_concat (xgetcwd (), file1, NULL);
but libraries should not call xalloc_die. */
char *cwd = getcwd (NULL, 0);
if (!cwd)
{
saved_errno = errno;
free_cwd (&saved_cwd);
errno = saved_errno;
return -1;
}
file1_alt = mfile_name_concat (cwd, file1, NULL);
if (!file1_alt)
{
saved_errno = errno;
free (cwd);
free_cwd (&saved_cwd);
errno = saved_errno;
return -1;
}
free (cwd); /* Reduced to case 3. */
}
else if (fd2 == AT_FDCWD && !IS_ABSOLUTE_FILE_NAME (file2)) /* Case 13. */
{
char *cwd = getcwd (NULL, 0);
if (!cwd)
{
saved_errno = errno;
free_cwd (&saved_cwd);
errno = saved_errno;
return -1;
}
file2_alt = mfile_name_concat (cwd, file2, NULL);
if (!file2_alt)
{
saved_errno = errno;
free (cwd);
free_cwd (&saved_cwd);
errno = saved_errno;
return -1;
}
free (cwd); /* Reduced to case 12. */
}
/* Cases 3, 12, 15a remain. Change to the correct directory. */
if (fchdir (fd1 == AT_FDCWD ? fd2 : fd1) != 0)
{
saved_errno = errno;
free_cwd (&saved_cwd);
if (file1 != file1_alt)
free (file1_alt);
else if (file2 != file2_alt)
free (file2_alt);
errno = saved_errno;
return -1;
}
/* Finally safe to perform the user's function, then clean up. */
err = func (file1_alt, file2_alt);
saved_errno = (err < 0 ? errno : 0);
if (file1 != file1_alt)
free (file1_alt);
else if (file2 != file2_alt)
free (file2_alt);
if (restore_cwd (&saved_cwd) != 0)
openat_restore_fail (errno);
free_cwd (&saved_cwd);
if (saved_errno)
errno = saved_errno;
return err;
}
#undef CALL_FUNC
#undef FUNC_RESULT
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