[PATCH 3/3] Check for write permission on FD based posix-clocks

[Torben Hohn <torbenh@gmx.de>]

pc_clock_settime() and pc_clock_adjtime() did not check
whether the fd was opened in write mode.

It was possible to set a clock, when we only had read
permissions.

for completeness, we would also need to check for Read permissions
on the read operations. but that would be a bit paranoid, probably.

Signed-off-by: Torben Hohn <torbenh@gmx.de>
Cc: Richard Cochran <richard.cochran@omicron.at>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/time/posix-clock.c |   14 ++++++++++++--
 1 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/time/posix-clock.c b/kernel/time/posix-clock.c
index 04498cb..25028dd 100644
--- a/kernel/time/posix-clock.c
+++ b/kernel/time/posix-clock.c
@@ -287,11 +287,16 @@ static int pc_clock_adjtime(clockid_t id, struct timex *tx)
 	if (err)
 		return err;
 
+	if ((cd.fp->f_mode & FMODE_WRITE) == 0) {
+		err = -EACCES;
+		goto out;
+	}
+
 	if (cd.clk->ops.clock_adjtime)
 		err = cd.clk->ops.clock_adjtime(cd.clk, tx);
 	else
 		err = -EOPNOTSUPP;
-
+out:
 	put_clock_desc(&cd);
 
 	return err;
@@ -344,11 +349,16 @@ static int pc_clock_settime(clockid_t id, const struct timespec *ts)
 	if (err)
 		return err;
 
+	if ((cd.fp->f_mode & FMODE_WRITE) == 0) {
+		err = -EACCES;
+		goto out;
+	}
+
 	if (cd.clk->ops.clock_settime)
 		err = cd.clk->ops.clock_settime(cd.clk, ts);
 	else
 		err = -EOPNOTSUPP;
-
+out:
 	put_clock_desc(&cd);
 
 	return err;
-- 
1.7.2.3