[PATCH 1/1] setitimer : Return -EFAULT if the user pointer "value" is NULL

[PATCH 1/1] setitimer : Return -EFAULT if the user pointer "value" is NULL

[Sasikantha babu]

Return -EFAULT if user  pointer "value" is  NULL.

In the current timer implementation  

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);

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

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

Signed-off-by: Sasikantha babu <sasikanth.v19@gmail.com>
---
 kernel/itimer.c |   17 ++++++++---------
 1 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/kernel/itimer.c b/kernel/itimer.c
index 22000c3..f356bdf 100644
--- a/kernel/itimer.c
+++ b/kernel/itimer.c
@@ -279,19 +279,18 @@ SYSCALL_DEFINE3(setitimer, int, which, struct itimerval __user *, value,
 		struct itimerval __user *, ovalue)
 {
 	struct itimerval set_buffer, get_buffer;
-	int error;
+	int error = -EFAULT;
 
 	if (value) {
 		if(copy_from_user(&set_buffer, value, sizeof(set_buffer)))
 			return -EFAULT;
-	} else
-		memset((char *) &set_buffer, 0, sizeof(set_buffer));
 
-	error = do_setitimer(which, &set_buffer, ovalue ? &get_buffer : NULL);
-	if (error || !ovalue)
-		return error;
+		error = do_setitimer(which, &set_buffer, ovalue ? &get_buffer : NULL);
+		if (error || !ovalue)
+			return error;
 
-	if (copy_to_user(ovalue, &get_buffer, sizeof(get_buffer)))
-		return -EFAULT;
-	return 0;
+		if (copy_to_user(ovalue, &get_buffer, sizeof(get_buffer)))
+			return -EFAULT;
+	}
+	return error;
 }
-- 
1.7.3.4

Re: [PATCH 1/1] setitimer : Return -EFAULT if the user pointer "value" is NULL

[Thomas Gleixner]

On Tue, 20 Mar 2012, Sasikantha babu wrote:

> Return -EFAULT if user  pointer "value" is  NULL.

In principle I agree, though this might break exisiting user space as
this behaviour has been there since Linux 1.1.52

So the right thing to do is to add a WARN_ONCE() in the else path and
schedule the removal of this "feature" for v3.6

> diff --git a/kernel/itimer.c b/kernel/itimer.c
> index 22000c3..f356bdf 100644
> --- a/kernel/itimer.c
> +++ b/kernel/itimer.c
> @@ -279,19 +279,18 @@ SYSCALL_DEFINE3(setitimer, int, which, struct itimerval __user *, value,
>  		struct itimerval __user *, ovalue)
>  {
>  	struct itimerval set_buffer, get_buffer;
> -	int error;
> +	int error = -EFAULT;

Instead of ripping the whole thing apart, it's way simpler to just do

	if (!value)
		return -EFAULT;

Thanks,

	tglx

[PATCH 1/1] setitimer : Return -EFAULT if the user pointer "value" is NULL

[Sasikantha babu]

Added WARN_ONCE() in the else path and schedule the removal of this "feature" for v3.6

Signed-off-by: Sasikantha babu <sasikanth.v19@gmail.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 d5dc80f..d943987 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -535,3 +535,12 @@ Why:	This driver provides support for USB storage devices like "USB
         (CONFIG_USB_STORAGE) which only drawback is the additional SCSI
         stack.
 Who:	Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
+
+----------------------------
+
+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@gmail.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