vfs: fix permission checking in sys_utimensat
If utimensat() is called with both times set to UTIME_NOW or one of them to
UTIME_NOW and the other to UTIME_OMIT, then it will update the file time
without any permission checking.
I don't think this can be used for anything other than a local DoS, but could
be quite bewildering at that (e.g. "Why was that large source tree rebuilt
when I didn't modify anything???")
This affects all kernels from 2.6.22, when the utimensat() syscall was
introduced.
Fix by doing the same permission checking as for the "times == NULL" case.
Thanks to Michael Kerrisk, whose utimensat-non-conformances-and-fixes.patch in
-mm also fixes this (and breaks other stuff), only he didn't realize the
security implications of this bug.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/utimes.c b/fs/utimes.c
index a2bef77..af059d5 100644
--- a/fs/utimes.c
+++ b/fs/utimes.c
@@ -40,9 +40,14 @@
#endif
+static bool nsec_special(long nsec)
+{
+ return nsec == UTIME_OMIT || nsec == UTIME_NOW;
+}
+
static bool nsec_valid(long nsec)
{
- if (nsec == UTIME_OMIT || nsec == UTIME_NOW)
+ if (nsec_special(nsec))
return true;
return nsec >= 0 && nsec <= 999999999;
@@ -119,7 +124,15 @@
newattrs.ia_mtime.tv_nsec = times[1].tv_nsec;
newattrs.ia_valid |= ATTR_MTIME_SET;
}
- } else {
+ }
+
+ /*
+ * If times is NULL or both times are either UTIME_OMIT or
+ * UTIME_NOW, then need to check permissions, because
+ * inode_change_ok() won't do it.
+ */
+ if (!times || (nsec_special(times[0].tv_nsec) &&
+ nsec_special(times[1].tv_nsec))) {
error = -EACCES;
if (IS_IMMUTABLE(inode))
goto mnt_drop_write_and_out;