On Wed, May 9, 2018 at 3:37 AM, Eric Biggers <ebigge...@gmail.com> wrote: > On Wed, Jan 03, 2018 at 10:53:14PM -0800, Eric Dumazet wrote: >> On Wed, 2018-01-03 at 21:13 -0800, Eric Dumazet wrote: >> > Note: all commands must start from beginning of the line in the email body. >> > >> > I guess skb_probe_transport_header() should be hardened to reject malicious >> > packets given by user space, instead of being gentle. >> >> Although bug triggered for this particular repro is in flow dissector >> :/ >> >> I will test : >> >> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c >> index >> 15ce300637650e17fcab7e378b20fe7972686d46..544bddf08e13c7f6e47aadc737244c9ba5af56b2 >> 100644 >> --- a/net/core/flow_dissector.c >> +++ b/net/core/flow_dissector.c >> @@ -976,8 +976,8 @@ bool __skb_flow_dissect(const struct sk_buff *skb, >> out_good: >> ret = true; >> >> - key_control->thoff = (u16)nhoff; >> out: >> + key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen); >> key_basic->n_proto = proto; >> key_basic->ip_proto = ip_proto; >> >> @@ -985,7 +985,6 @@ bool __skb_flow_dissect(const struct sk_buff *skb, >> >> out_bad: >> ret = false; >> - key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen); >> goto out; >> } >> EXPORT_SYMBOL(__skb_flow_dissect); > > Fix for this was commit d0c081b49137cd: > > #syz fix: flow_dissector: properly cap thoff field > > But a crash with the same signature is still occurring, so it should > eventually > get reported again. C reproducer is here, it works on Linus' tree (commit > 036db8bd963): https://syzkaller.appspot.com/text?tag=ReproC&x=105b1ae7800000
This appears to be a separate issue. This reproducer requires a setsockopt SOL_SOCKET/SO_TIMESTAMPING to trigger the use-after-free. And the freed path also points at a timestamping skb: [ 31.963619] Freed by task 2672: [ 31.964006] __kasan_slab_free+0x125/0x170 [ 31.964509] kfree+0x8b/0x1a0 [ 31.964875] skb_free_head+0x6f/0xa0 [ 31.965314] skb_release_data+0x420/0x5a0 [ 31.965802] skb_release_all+0x46/0x60 [ 31.966260] kfree_skb+0x91/0x1c0 [ 31.966669] __skb_complete_tx_timestamp+0x2e9/0x3d0 [ 31.967273] __skb_tstamp_tx+0x3b3/0x620 [ 31.967774] __dev_queue_xmit+0xed5/0x1a20 [ 31.968300] packet_sendmsg+0x36fd/0x5400 [ 31.968821] sock_sendmsg+0xc0/0x100 [ 31.969284] ___sys_sendmsg+0x367/0x880 [ 31.969777] __sys_sendmmsg+0x178/0x410 [ 31.970267] __x64_sys_sendmmsg+0x99/0x100 [ 31.970789] do_syscall_64+0x9a/0x2c0 [ 31.971260] entry_SYSCALL_64_after_hwframe+0x44/0xa9 The data skb itself is zero bytes, it appears.
