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Subject[PATCH] fix stack memory content leak via UNAME26
Calling uname() with the UNAME26 personality set allows a leak of kernel
stack contents. This fixes it by initializing the stack buffer to zero,
defensively calculating the length of copy_to_user() call, and making
the len argument unsigned.

CVE-2012-0957

Reported-by: Brad Spengler <spender@grsecurity.net>
Cc: stable@vger.kernel.org
Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
kernel/sys.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/kernel/sys.c b/kernel/sys.c
index c5cb5b9..6329092 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1265,13 +1265,13 @@ DECLARE_RWSEM(uts_sem);
* Work around broken programs that cannot handle "Linux 3.0".
* Instead we map 3.x to 2.6.40+x, so e.g. 3.0 would be 2.6.40
*/
-static int override_release(char __user *release, int len)
+static int override_release(char __user *release, size_t len)
{
int ret = 0;
- char buf[65];
+ char buf[65] = { 0 };
+ const char *rest = UTS_RELEASE;

if (current->personality & UNAME26) {
- char *rest = UTS_RELEASE;
int ndots = 0;
unsigned v;

@@ -1283,7 +1283,9 @@ static int override_release(char __user *release, int len)
rest++;
}
v = ((LINUX_VERSION_CODE >> 8) & 0xff) + 40;
- snprintf(buf, len, "2.6.%u%s", v, rest);
+ snprintf(buf, sizeof(buf), "2.6.%u%s", v, rest);
+ if (sizeof(buf) < len)
+ len = sizeof(buf);
ret = copy_to_user(release, buf, len);
}
return ret;
--
1.7.9.5

--
Kees Cook
Chrome OS Security


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