Commit 02c6be61 authored May 01, 2008 by Miklos Szeredi Committed by Linus Torvalds May 01, 2008

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>

parent 2850699c

fs/utimes.c

+15 −2

Original line number	Diff line number	Diff line
		@@ -40,9 +40,14 @@ asmlinkage long sys_utime(char __user filename, struct utimbuf __user times)

		#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 @@ long do_utimes(int dfd, char __user filename, struct timespec times, int flags
		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;