posix-clocks: Check write permissions in posix syscalls

pc_clock_settime() and pc_clock_adjtime() do not check whether the fd
was opened in write mode, so a clock can be set with a read only fd.

[ tglx: We deliberately do not return -EPERM as we want this to be
  	distingushable from the capability based permission check ]

Signed-off-by: Torben Hohn <torbenh@gmx.de>
LKML-Reference: <1299173174-348-4-git-send-email-torbenh@gmx.de>
Cc: Richard Cochran <richard.cochran@omicron.at>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 12 insertions, 2 deletions

diff --git a/kernel/time/posix-clock.c b/kernel/time/posix-clock.c
index 04498cbf600..25028dd4fa1 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;