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0809fed0d6
This fixes CVE-2015-7550. There's a race between keyctl_read() and keyctl_revoke(). If the revoke happens between keyctl_read() checking the validity of a key and the key's semaphore being taken, then the key type read method will see a revoked key. This causes a problem for the user-defined key type because it assumes in its read method that there will always be a payload in a non-revoked key and doesn't check for a NULL pointer. Fix this by making keyctl_read() check the validity of a key after taking semaphore instead of before. I think the bug was introduced with the original keyrings code. This was discovered by a multithreaded test program generated by syzkaller (http://github.com/google/syzkaller). Here's a cleaned up version: #include <sys/types.h> #include <keyutils.h> #include <pthread.h> void *thr0(void *arg) { key_serial_t key = (unsigned long)arg; keyctl_revoke(key); return 0; } void *thr1(void *arg) { key_serial_t key = (unsigned long)arg; char buffer[16]; keyctl_read(key, buffer, 16); return 0; } int main() { key_serial_t key = add_key("user", "%", "foo", 3, KEY_SPEC_USER_KEYRING); pthread_t th[5]; pthread_create(&th[0], 0, thr0, (void *)(unsigned long)key); pthread_create(&th[1], 0, thr1, (void *)(unsigned long)key); pthread_create(&th[2], 0, thr0, (void *)(unsigned long)key); pthread_create(&th[3], 0, thr1, (void *)(unsigned long)key); pthread_join(th[0], 0); pthread_join(th[1], 0); pthread_join(th[2], 0); pthread_join(th[3], 0); return 0; } Build as: cc -o keyctl-race keyctl-race.c -lkeyutils -lpthread Run as: while keyctl-race; do :; done as it may need several iterations to crash the kernel. The crash can be summarised as: BUG: unable to handle kernel NULL pointer dereference at 0000000000000010 IP: [<ffffffff81279b08>] user_read+0x56/0xa3 ... Call Trace: [<ffffffff81276aa9>] keyctl_read_key+0xb6/0xd7 [<ffffffff81277815>] SyS_keyctl+0x83/0xe0 [<ffffffff815dbb97>] entry_SYSCALL_64_fastpath+0x12/0x6f Change-Id: Id4a5e47860162f62c94bb66728ca9e712f9d89c2 Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: David Howells <dhowells@redhat.com> Tested-by: Dmitry Vyukov <dvyukov@google.com> Cc: stable@vger.kernel.org Signed-off-by: James Morris <james.l.morris@oracle.com> |
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| .. | ||
| encrypted-keys | ||
| compat.c | ||
| gc.c | ||
| internal.h | ||
| key.c | ||
| keyctl.c | ||
| keyring.c | ||
| Makefile | ||
| permission.c | ||
| proc.c | ||
| process_keys.c | ||
| request_key.c | ||
| request_key_auth.c | ||
| sysctl.c | ||
| trusted.c | ||
| trusted.h | ||
| user_defined.c | ||