[tip:timers/core] posix-clocks: Check write permissions in posix syscalls

[tip-bot for Torben Hohn]

Commit-ID:  6e6823d17b157f185be09f4c70181299f9273f0b
Gitweb:     http://git.kernel.org/tip/6e6823d17b157f185be09f4c70181299f9273f0b
Author:     Torben Hohn <torbenh@xxxxxx>
AuthorDate: Thu, 3 Mar 2011 18:26:14 +0100
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Sat, 12 Mar 2011 21:27:07 +0100

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@xxxxxx>
LKML-Reference: <1299173174-348-4-git-send-email-torbenh@xxxxxx>
Cc: Richard Cochran <richard.cochran@xxxxxxxxxx>
Cc: John Stultz <johnstul@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 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;
--
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