From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1525882326; cv=none; d=google.com; s=arc-20160816; b=ybJovT//K3B4JKqJ9hhEc92On9i1cU/cRO6TvPBp/cqRmhs8BcyGd67lTH4vqmmsyr +d2JfaBmuTaArdeDHISU6bba8+I486wZR47etDc9AlV1Sr/9kx6uEhG/U7ASFV8YZNWw b67dM+eYFl5WORjMUpkVmNoYXe3gQBDFaEroq7mJaIpkWBywya/SodDIUF8MOxnwtOxh koyG4Y3ZxvN/Lf5x82t2Qm3Lck21gG0i4FKlJqWS01PuLZcyzeWxiXK0qxD2PL30m6GA uuhj7d2IsAsACJrUXgkLJ0SAO89L5HeAa/TdNjZBhZqRmBQamHYvwffB0Tl9ijq9U1av FKuA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=cc:to:subject:message-id:date:from:references:in-reply-to :mime-version:dkim-signature:arc-authentication-results; bh=sNoddvFokU5OQf/EACgG0Dl7RrTLtu192Q5ap+EEXuA=; b=NlxVwyCLtoRcOw4Wj6Jgs7MpquJj9GW39pimYawzQXHnSeh4Smx4bqMMn9VykObg7c WShIz0imRW+Nq8JlYTkx/gAXrxFgTTY0eUQGUKi5eJ1reu/n7SELsqOBpjhl4fGe9saF BWZqYF9eMKdb7GZ4ZRLUti+iVNoHhDObR/Xd6SUYZnQckdAzpD+lfPlNSNRH4oZa67W0 TZp51BCtvkJCrr/S5ok1iqjLq/zz0pZ01mFXSklrZBDpx0RAmqTpKZ4LDDnHACLDarMM pY1w/l02e2NwPM21L6tHALwxXmXJYq92qnx+Kbuuc9fQo9Taj95LMQ+OkhhY+pQtKxMy bOAA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=RNEtzlyx; spf=pass (google.com: domain of willemdebruijn.kernel@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=willemdebruijn.kernel@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=RNEtzlyx; spf=pass (google.com: domain of willemdebruijn.kernel@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=willemdebruijn.kernel@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com X-Google-Smtp-Source: AB8JxZqqDsL5FpH6vpx/StMY/w0qBINVOdoqyzPoHnQjzW5+/nMUwo2IRSWLPhkcUg0iHcoQWHIe9s+9Sg55Rd6BRCs= MIME-Version: 1.0 In-Reply-To: <20180509073754.GG711@sol.localdomain> References: <94eb2c0ce3aa27cfa40561ec2dc3@google.com> <1515048794.131759.4.camel@gmail.com> <20180509073754.GG711@sol.localdomain> From: Willem de Bruijn Date: Wed, 9 May 2018 12:11:25 -0400 Message-ID: Subject: Re: KASAN: use-after-free Read in __dev_queue_xmit To: Eric Biggers Cc: Eric Dumazet , Eric Dumazet , syzbot , alexander.deucher@amd.com, Andrey Konovalov , Anoob Soman , chris@chris-wilson.co.uk, David Miller , "Reshetova, Elena" , Greg Kroah-Hartman , Kees Cook , LKML , Mike Maloney , mchehab@kernel.org, netdev , "Rosen, Rami" , Sowmini Varadhan , syzkaller-bugs@googlegroups.com, Willem de Bruijn Content-Type: text/plain; charset="UTF-8" X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1588636556567233283?= X-GMAIL-MSGID: =?utf-8?q?1600003586944703621?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, May 9, 2018 at 3:37 AM, Eric Biggers 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.