[PATCH] utime(s): Honour CAP_FOWNER when times==NULL

[Satyam Sharma <ssatyam@cse.iitk.ac.in>]

[PATCH] utime(s): Honour CAP_FOWNER when times==NULL

do_utimes() does not honour CAP_FOWNER when times==NULL.
Trivial and obvious one-line fix.

Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>

---

BTW this bug was hidden by the fact that we call vfs_permission() from the
code below (for) this condition. vfs_permission() inevitably degenerates to
generic_permission() which returns 0 (success) for CAP_DAC_OVERRIDE.

However, a privileged process that has released CAP_DAC_OVERRIDE (but carries
CAP_FOWNER) would still get bit by this issue. There is a sample userspace
program (with instructions on how to reproduce) available at:

http://www.cse.iitk.ac.in/users/ssatyam/test.c

 fs/utimes.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/utimes.c b/fs/utimes.c
index b3c8895..83a7e69 100644
--- a/fs/utimes.c
+++ b/fs/utimes.c
@@ -106,7 +106,7 @@ long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags
                 if (IS_IMMUTABLE(inode))
                         goto dput_and_out;
 
-		if (current->fsuid != inode->i_uid) {
+		if ((current->fsuid != inode->i_uid) && !capable(CAP_FOWNER)) {
 			if (f) {
 				if (!(f->f_mode & FMODE_WRITE))
 					goto dput_and_out;