Commit 8999dc89 authored Apr 28, 2020 by YueHaibing Committed by David S. Miller Apr 28, 2020

net/x25: Fix null-ptr-deref in x25_disconnect



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: 4becb7ee ("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>

parent caec6619

net/x25/x25_subr.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -357,11 +357,13 @@ void x25_disconnect(struct sock *sk, int reason, unsigned char cause,
		sk->sk_state_change(sk);
		sock_set_flag(sk, SOCK_DEAD);
		}
		if (x25->neighbour) {
		read_lock_bh(&x25_list_lock);
		x25_neigh_put(x25->neighbour);
		x25->neighbour = NULL;
		read_unlock_bh(&x25_list_lock);
		}
		}

		/*
		* Clear an own-rx-busy condition and tell the peer about this, provided

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