[tip:sched/urgent] sched: Fix information leak in sys_sched_getattr()

[tip-bot for Vegard Nossum]

Commit-ID:  4efbc454ba68def5ef285b26ebfcfdb605b52755
Gitweb:     http://git.kernel.org/tip/4efbc454ba68def5ef285b26ebfcfdb605b52755
Author:     Vegard Nossum <vegard.nossum@xxxxxxxxxx>
AuthorDate: Sun, 16 Feb 2014 22:24:17 +0100
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 21 Feb 2014 21:27:10 +0100

sched: Fix information leak in sys_sched_getattr()

We're copying the on-stack structure to userspace, but forgot to give
the right number of bytes to copy. This allows the calling process to
obtain up to PAGE_SIZE bytes from the stack (and possibly adjacent
kernel memory).

This fix copies only as much as we actually have on the stack
(attr->size defaults to the size of the struct) and leaves the rest of
the userspace-provided buffer untouched.

Found using kmemcheck + trinity.

Fixes: d50dde5a10f30 ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Cc: Dario Faggioli <raistlin@xxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1392585857-10725-1-git-send-email-vegard.nossum@xxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 33d030a..a6e7470 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3786,7 +3786,7 @@ static int sched_read_attr(struct sched_attr __user *uattr,
 		attr->size = usize;
 	}
 
-	ret = copy_to_user(uattr, attr, usize);
+	ret = copy_to_user(uattr, attr, attr->size);
 	if (ret)
 		return -EFAULT;
 
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