From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1525893735; cv=none; d=google.com; s=arc-20160816; b=yDtczbXhu0pj+fB1qJkCexz7KKH0TuYqS+dFHIvsdWsJQCYHSFIRm0kIZ6V9bO9Mg4 RKPhcIXhmtVbEwXExd42/VqXCMEabMbMTB042qh69HIhYdjOcLR2/yBqVLU7WxVL/a3N wk8OM7eJFUWZpJ0+K6hL7w2woJ6prE6Jn4ZhxmlHBNkIb1jesX1vjPVMXaRQnVJbACtm qI8fOz3r3CMizgcmNr33HP5PFVFNW4b6DABhgS1NQfpY7kkLnQ8ais7dXj+QvnsjB3QB 5k63TvYmLMu829l/VyngAmKcJFfz5EMo3IdlpfXFy6Y1KN4olKHOOKjKPNcUO8EgZQiG PKug== 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=zeTRHWpvPK0wCoZ+ES4041KrQUnqw+utrMIXhFmUrbc=; b=EMjUZ+DcUJ6gIDjfTUopeSWNAXJETfVwTj338VGFORHLcII6E1oSI28uAOsKpF1tad IbHcvD8QZQh20kR3gMciuY++eZIvJzSq1CJTf/3hVMieHbYcDZi0dv8Z38gFENq/NYFO ldJ6gWzll4zzYSM8X6+cgw0i4z5+hr1WNFpFkkrrXoFtIWrojCFfiy/50A8qY9gy38Z+ jbqkaiashirF1Ph8jyklv54tvkh7Qe/E7YqfG6QhMz9Mhiewx0TnqXEXxbArJgudsC1Q vc1n/BFJlXKFS04gJY1+M7k4lEmGZCM4k2rfRtl7ELXIn9BrdhPafFdTfjK0wANmdN71 aJEg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=ql3E3AsJ; 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=ql3E3AsJ; 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: AB8JxZrlchRQ6DX5BgHiJNvbebXJNUrqNtAAruffxtJW1s8gNSiF0MfFVxzDMBnLZCgNBxwVW2iA8+FI4BDt5Xgta+A= MIME-Version: 1.0 In-Reply-To: References: <94eb2c0ce3aa27cfa40561ec2dc3@google.com> <1515048794.131759.4.camel@gmail.com> <20180509073754.GG711@sol.localdomain> From: Willem de Bruijn Date: Wed, 9 May 2018 15:21:33 -0400 Message-ID: Subject: Re: KASAN: use-after-free Read in __dev_queue_xmit To: Eric Biggers Cc: 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?1600015549393663815?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, May 9, 2018 at 12:38 PM, Willem de Bruijn wrote: >>> 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 > > This is a rare path taken when the timestamp skb cannot be queued > onto the socket (likely because of insufficient rcvbuf). > > Somehow, freeing the timestamp skb triggers this use-after-free in > the original skb from which the timestamp was cloned. As if there > is a bug in the shared info dataref. Indeed. The skb shared info struct is zeroed by dev_validate_header as a result of dev->hard_header_len exceeding skb->end - skb->data. Not exactly sure yet how this can happen. The hard header length space is accounted for during allocation as reserved memory. But, packet_alloc_skb does call skb_reserve(), moving skb->data effectively beyond this reserved region. It may be incorrect to pass skb->data to dev_validate_header, as that does not point to the start of the ll_header anymore. Still figuring out what the right fix is..