From: YueHaibing yuehaibing@huawei.com
commit 8999dc89497ab1c80d0718828e838c7cd5f6bffe upstream.
We should check null before do x25_neigh_put in x25_disconnect, otherwise may cause null-ptr-deref like this:
#include <sys/socket.h> #include <linux/x25.h>
int main() { int sck_x25; sck_x25 = socket(AF_X25, SOCK_SEQPACKET, 0); close(sck_x25); return 0; }
BUG: kernel NULL pointer dereference, address: 00000000000000d8 CPU: 0 PID: 4817 Comm: t2 Not tainted 5.7.0-rc3+ #159 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3- RIP: 0010:x25_disconnect+0x91/0xe0 Call Trace: x25_release+0x18a/0x1b0 __sock_release+0x3d/0xc0 sock_close+0x13/0x20 __fput+0x107/0x270 ____fput+0x9/0x10 task_work_run+0x6d/0xb0 exit_to_usermode_loop+0x102/0x110 do_syscall_64+0x23c/0x260 entry_SYSCALL_64_after_hwframe+0x49/0xb3
Reported-by: syzbot+6db548b615e5aeefdce2@syzkaller.appspotmail.com Fixes: 4becb7ee5b3d ("net/x25: Fix x25_neigh refcnt leak when x25 disconnect") Signed-off-by: YueHaibing yuehaibing@huawei.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/x25/x25_subr.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
--- a/net/x25/x25_subr.c +++ b/net/x25/x25_subr.c @@ -363,10 +363,12 @@ void x25_disconnect(struct sock *sk, int sk->sk_state_change(sk); sock_set_flag(sk, SOCK_DEAD); } - read_lock_bh(&x25_list_lock); - x25_neigh_put(x25->neighbour); - x25->neighbour = NULL; - read_unlock_bh(&x25_list_lock); + if (x25->neighbour) { + read_lock_bh(&x25_list_lock); + x25_neigh_put(x25->neighbour); + x25->neighbour = NULL; + read_unlock_bh(&x25_list_lock); + } }
/*