Date: Sat, 01 Jun 2019 15:01:42 +0000 From: "Bjoern A. Zeeb" <bz@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r348494 - head/sys/netinet Message-ID: <8F8F89D8-62A1-4EEA-9457-F511AF67D893@FreeBSD.org> In-Reply-To: <201906011457.x51Evgc9036752@repo.freebsd.org> References: <201906011457.x51Evgc9036752@repo.freebsd.org>
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On 1 Jun 2019, at 14:57, Bjoern A. Zeeb wrote: > Author: bz > Date: Sat Jun 1 14:57:42 2019 > New Revision: 348494 > URL: https://svnweb.freebsd.org/changeset/base/348494 > > Log: > After parts of the locking fixes in r346595, syzkaller found > another one in udp_output(). This one is a race condition. > We do check on the laddr and lport without holding a lock in > order to determine whether we want a read or a write lock > (this is in the "sendto/sendmsg" cases where addr (sin) is given). > > Instrumenting the kernel showed that after taking the lock, we > had bound to a local port from a parallel thread on the same socket. > > If we find that case, unlock, and retry again. Taking the write > lock would not be a problem in first place (apart from killing some > parallelism). However the retry is needed as later on based on > similar condition checks we do acquire the pcbinfo lock and if the > conditions have changed, we might find ourselves with a lock > inconsistency, hence at the end of the function when trying to > unlock, hitting the KASSERT. > > Reported by: syzbot+bdf4caa36f3ceeac198f@syzkaller.appspotmail.com > Reviewed by: markj > MFC after: 6 weeks > Event: Waterloo Hackathon 2019 Differential Revision: https://reviews.freebsd.org/D20338
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