Date: Tue, 19 Feb 2019 15:46:43 +0000 (UTC) From: Mark Johnston <markj@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r344278 - head/sys/kern Message-ID: <201902191546.x1JFkhZq032336@repo.freebsd.org>
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Author: markj Date: Tue Feb 19 15:46:43 2019 New Revision: 344278 URL: https://svnweb.freebsd.org/changeset/base/344278 Log: Move a racy assertion in filt_pipewrite(). EVFILT_WRITE knotes for pipes live on the knlist for the other end of the pipe. Since they do not hold a reference on the corresponding file structure, they may be removed from the knlist by pipeclose() while still remaining active. In this case, there is no knlist lock acquired before filt_pipewrite() is called, so the assertion fails. Fix the problem by first checking whether that end of the pipe has been closed. These checks are memory safe since the knote holds a reference on one end of the pipe, and the pipe structure is not freed until both ends are closed. The checks are not racy since PIPE_EOF is never cleared after being set, and pipe_present is never set back to PIPE_ACTIVE after pipeclose() has been called. PR: 235640 Reported and tested by: pho Reviewed by: kib MFC after: 2 weeks Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D19224 Modified: head/sys/kern/sys_pipe.c Modified: head/sys/kern/sys_pipe.c ============================================================================== --- head/sys/kern/sys_pipe.c Tue Feb 19 12:45:37 2019 (r344277) +++ head/sys/kern/sys_pipe.c Tue Feb 19 15:46:43 2019 (r344278) @@ -1741,15 +1741,19 @@ static int filt_pipewrite(struct knote *kn, long hint) { struct pipe *wpipe; - + + /* + * If this end of the pipe is closed, the knote was removed from the + * knlist and the list lock (i.e., the pipe lock) is therefore not held. + */ wpipe = kn->kn_hook; - PIPE_LOCK_ASSERT(wpipe, MA_OWNED); if (wpipe->pipe_present != PIPE_ACTIVE || (wpipe->pipe_state & PIPE_EOF)) { kn->kn_data = 0; kn->kn_flags |= EV_EOF; return (1); } + PIPE_LOCK_ASSERT(wpipe, MA_OWNED); kn->kn_data = (wpipe->pipe_buffer.size > 0) ? (wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) : PIPE_BUF; if (wpipe->pipe_state & PIPE_DIRECTW)
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