Calling uname() with the UNAME26 personality set allows a leak of kernel
stack contents. This fixes it by defensively calculating the length of
copy_to_user() call, making the len argument unsigned, and initializing
the stack buffer to zero (now technically unneeded, but hey, overkill).
CVE-2012-0957
Reported-by: PaX Team <pagee...@freemail.hu>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Andi Kleen <a...@linux.intel.com>
Cc: PaX Team <pagee...@freemail.hu>
Cc: Brad Spengler <spen...@grsecurity.net>
Cc: sta...@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
v3:
- use scnprintf, suggested by Andrew Morton.
- proactively handle impossible len == 0 case.
v2:
- corrected credit to PaX Team.
- moved stack clearing into if case to avoid penalty to common case.
---
kernel/sys.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/kernel/sys.c b/kernel/sys.c
index c5cb5b9..01865c6 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1265,15 +1265,16 @@ 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];
if (current->personality & UNAME26) {
- char *rest = UTS_RELEASE;
+ const char *rest = UTS_RELEASE;
+ char buf[65] = { 0 };
int ndots = 0;
unsigned v;
+ size_t copy;
while (*rest) {
if (*rest == '.' && ++ndots >= 3)
@@ -1283,8 +1284,9 @@ 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);
- ret = copy_to_user(release, buf, len);
+ copy = min(sizeof(buf), max_t(size_t, 1, len));
+ copy = scnprintf(buf, copy, "2.6.%u%s", v, rest);
+ ret = copy_to_user(release, buf, copy + 1);
}
return ret;
}
--
1.7.9.5
--
Kees Cook
Chrome OS Security
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