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kernel/sys.c: 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 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 <pageexec@freemail.hu>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: PaX Team <pageexec@freemail.hu>
Cc: Brad Spengler <spender@grsecurity.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kees Cook 2012-10-19 13:56:51 -07:00 committed by Linus Torvalds
parent 1d46e232f8
commit 2702b1526c
1 changed files with 7 additions and 5 deletions
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12
kernel/sys.c
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@ -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;
}