From: Tadeusz Struk > Sent: 08 March 2022 00:02 > > Syzbot found a kernel bug in the ipv6 stack: > LINK: https://syzkaller.appspot.com/bug?id=205d6f11d72329ab8d62a610c44c5e7e25415580 > > The reproducer triggers it by sending an invalid message via sendmmsg() call, > which triggers skb_over_panic, and crashes the kernel: > > skbuff: skb_over_panic: text:ffffffff84647fb4 len:65575 put:65575 > head:ffff888109ff0000 data:ffff888109ff0088 tail:0x100af end:0xfec0 > dev:<NULL> > > ------------[ cut here ]------------ > kernel BUG at net/core/skbuff.c:113! > PREEMPT SMP KASAN > CPU: 1 PID: 1818 Comm: repro Not tainted 5.17.0-rc7-dirty #9 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35 > RIP: 0010:skb_panic+0x173/0x175 > RSP: 0018:ffffc900015bf3b8 EFLAGS: 00010282 > RAX: 0000000000000090 RBX: ffff88810e848c80 RCX: 0000000000000000 > RDX: ffff88810fd84300 RSI: ffffffff814fa5ef RDI: fffff520002b7e69 > RBP: ffffc900015bf420 R08: 0000000000000090 R09: 0000000000000000 > R10: ffffffff814f55f4 R11: 203a666675626b73 R12: ffffffff855bff80 > R13: ffffffff84647fb4 R14: 0000000000010027 R15: ffffffff855bf420 > FS: 0000000000c8b3c0(0000) GS:ffff88811b100000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000020000040 CR3: 0000000106b68000 CR4: 0000000000150ea0 > Call Trace: > <TASK> > skb_put.cold+0x23/0x23 > __ip6_append_data.isra.0.cold+0x396/0xe3a > ip6_append_data+0x1e5/0x320 > rawv6_sendmsg.cold+0x1618/0x2ba9 > inet_sendmsg+0x9e/0xe0 > sock_sendmsg+0xd7/0x130 > ____sys_sendmsg+0x381/0x8a0 > ___sys_sendmsg+0x100/0x170 > __sys_sendmmsg+0x26c/0x3b7 > __x64_sys_sendmmsg+0xb2/0xbd > do_syscall_64+0x35/0xb0 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > The reproducer can be found here: > LINK: https://syzkaller.appspot.com/text?tag=ReproC&x=1648c83fb00000 > This can be fixed by increasing the alloclen in case it is smaller than > fraglen in __ip6_append_data(). > > > Reported-by: syzbot+e223cf47ec8ae183f2a0@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Tadeusz Struk <tadeusz.struk@xxxxxxxxxx> > --- > net/ipv6/ip6_output.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c > index 4788f6b37053..622345af323e 100644 > --- a/net/ipv6/ip6_output.c > +++ b/net/ipv6/ip6_output.c > @@ -1629,6 +1629,13 @@ static int __ip6_append_data(struct sock *sk, > err = -EINVAL; > goto error; > } > + if (unlikely(alloclen < fraglen)) { > + if (printk_ratelimit()) > + pr_warn("%s: wrong alloclen: %d, fraglen: %d", > + __func__, alloclen, fraglen); > + alloclen = fraglen; > + } > + Except that is a valid case, see a few lines higher: alloclen = min_t(int, fraglen, MAX_HEADER); pagedlen = fraglen - alloclen; You need to report the input values that cause the problem later on. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
