+2020-02-13 Paul Eggert <eggert@cs.ucla.edu>
+
+ fchmodat, lchmod: port to buggy Linux filesystems
+ Problem reported by Florian Weimer in:
+ https://www.sourceware.org/ml/libc-alpha/2020-02/msg00534.html
+ * lib/fchmodat.c (fchmodat):
+ * lib/lchmod.c (lchmod):
+ Don’t assume that chmod on the O_PATH-opened fd will do
+ the right thing on a symbolic link.
+ * lib/fchmodat.c (fchmodat):
+ Don’t attempt to special-case
+ any flag value other than AT_SYMLINK_NOFOLLOW.
+
2020-02-11 Paul Eggert <eggert@cs.ucla.edu>
lchmod: pacify Coverity CID 1491216
int
fchmodat (int dir, char const *file, mode_t mode, int flags)
{
- if (flags & AT_SYMLINK_NOFOLLOW)
+ if (flags == AT_SYMLINK_NOFOLLOW)
{
-# ifdef O_PATH
+ struct stat st;
+
+# if defined O_PATH && defined AT_EMPTY_PATH
int fd = openat (dir, file, O_PATH | O_NOFOLLOW | O_CLOEXEC);
if (fd < 0)
return fd;
+
+ /* Use fstatat because fstat does not work on O_PATH descriptors
+ before Linux 3.6. */
+ if (fstatat (fd, "", &st, AT_EMPTY_PATH) != 0)
+ {
+ int stat_errno = errno;
+ close (fd);
+ errno = stat_errno;
+ return -1;
+ }
+ if (S_ISLNK (st.st_mode))
+ {
+ close (fd);
+ errno = EOPNOTSUPP;
+ return -1;
+ }
+
static char const fmt[] = "/proc/self/fd/%d";
char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
sprintf (buf, fmt, fd);
errno = chmod_errno;
return chmod_result;
}
- /* /proc is not mounted; fall back on racy implementation. */
-# endif
-
- struct stat st;
+ /* /proc is not mounted. */
+# else
int fstatat_result = fstatat (dir, file, &st, AT_SYMLINK_NOFOLLOW);
if (fstatat_result != 0)
return fstatat_result;
errno = EOPNOTSUPP;
return -1;
}
- flags &= ~AT_SYMLINK_NOFOLLOW;
+# endif
+ /* Fall back on chmod, despite the race. */
+ flags = 0;
}
return orig_fchmodat (dir, file, mode, flags);
#if HAVE_FCHMODAT
return fchmodat (AT_FDCWD, file, mode, AT_SYMLINK_NOFOLLOW);
#else
-# if defined O_PATH && defined AT_FDCWD
+# if defined AT_FDCWD && defined O_PATH && defined AT_EMPTY_PATH
int fd = openat (AT_FDCWD, file, O_PATH | O_NOFOLLOW | O_CLOEXEC);
if (fd < 0)
return fd;
+
+ /* Use fstatat because fstat does not work on O_PATH descriptors
+ before Linux 3.6. */
+ struct stat st;
+ if (fstatat (fd, "", &st, AT_EMPTY_PATH) != 0)
+ {
+ int stat_errno = errno;
+ close (fd);
+ errno = stat_errno;
+ return -1;
+ }
+ if (S_ISLNK (st.st_mode))
+ {
+ close (fd);
+ errno = EOPNOTSUPP;
+ return -1;
+ }
+
static char const fmt[] = "/proc/self/fd/%d";
char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
sprintf (buf, fmt, fd);
errno = chmod_errno;
return chmod_result;
}
- /* /proc is not mounted; fall back on racy implementation. */
-# endif
-
-# if HAVE_LSTAT
+ /* /proc is not mounted. */
+# elif HAVE_LSTAT
struct stat st;
int lstat_result = lstat (file, &st);
if (lstat_result != 0)
}
# endif
+ /* Fall back on chmod, despite the race. */
return chmod (file, mode);
#endif
}