linux-kernel - [PATCH V2] Feature removal: schedule removal of setitimer accepting user's NULL pointer and set timer with 0 value

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Date:	Fri, 30 Mar 2012 19:29:52 +0530
From:	Sasikantha babu <sasikanth.v19@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org,
	Sasikantha babu <sasikanth.v19@...il.com>
Subject: [PATCH V2] Feature removal: schedule removal of setitimer accepting user's NULL pointer and set timer with 0 value

sys_setitimer accepts the user pointer NULL and sets the time with 0 secs and 0 micro secs  i.e.

setitimer (which, NULL, NULL)

is equal to

timer.it_value.tv_sec = 0;
timer.it_value.tv_usec = 0;
timer.it_interval.tv_sec = 0;
timer.it_interval.tv_usec = 0;

setitimer (which, &timer, NULL);

But setitimer man page says "The function setitimer() sets the specified timer to the value in new_value".

If user pass new_value as NULL, kernel should not set timer with tv_sec = 0 and tv_usec = 0, instead return -EFAULT.

To avoid breaking exisiting user space added WARN_ONCE() if user pointer is NULL and 
scheduled the removal of this "feature" for v3.6

Signed-off-by: Sasikantha babu <sasikanth.v19@...il.com>
---
 Documentation/feature-removal-schedule.txt |    9 +++++++++
 kernel/itimer.c                            |    5 ++++-
 2 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 0cad480..bc552ce 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -529,3 +529,12 @@ When:	3.5
 Why:	The old kmap_atomic() with two arguments is deprecated, we only
 	keep it for backward compatibility for few cycles and then drop it.
 Who:	Cong Wang <amwang@...hat.com>
+
+-------------------------------
+
+What:  setitimer accepts user's NULL pointer - interval timer pointer 
+When:  3.6
+Why:   setitimer is not returning -EFAULT if user point is NULL. If user passes
+       "struct itimerval *value" as NULL instead of returning -EFAULT it 
+       sets value of an interval timer to 0 secs and 0 micro secs.
+Who:   Sasikantha Babu <sasikanth.v19@...il.com> 
diff --git a/kernel/itimer.c b/kernel/itimer.c
index 22000c3..10f3cfb 100644
--- a/kernel/itimer.c
+++ b/kernel/itimer.c
@@ -284,8 +284,11 @@ SYSCALL_DEFINE3(setitimer, int, which, struct itimerval __user *, value,
 	if (value) {
 		if(copy_from_user(&set_buffer, value, sizeof(set_buffer)))
 			return -EFAULT;
-	} else
+	} else {
 		memset((char *) &set_buffer, 0, sizeof(set_buffer));
+		WARN_ONCE (!value, "setitimer: Support for handling NULL user pointer "
+				    " will be removed");
+	}
 
 	error = do_setitimer(which, &set_buffer, ovalue ? &get_buffer : NULL);
 	if (error || !ovalue)
-- 
1.7.3.4

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