Date: Mon, 20 Jun 2011 18:08:52 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-7@freebsd.org Subject: svn commit: r223344 - stable/7/sys/netinet Message-ID: <201106201808.p5KI8qYU060393@svn.freebsd.org>
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Author: jhb Date: Mon Jun 20 18:08:52 2011 New Revision: 223344 URL: http://svn.freebsd.org/changeset/base/223344 Log: MFC 221346,223049: Handle a rare edge case with nearly full TCP receive buffers. If a TCP buffer fills up causing the remote sender to enter into persist mode, but there is still room available in the receive buffer when a window probe arrives (either due to window scaling, or due to the local application very slowing draining data from the receive buffer), then the single byte of data in the window probe is accepted. However, this can cause rcv_nxt to be greater than rcv_adv. This condition will only last until the next ACK packet is pushed out via tcp_output(), and since the previous ACK advertised a zero window, the ACK should be pushed out while the TCP pcb is write-locked. To guarantee this, advance the advertised window (rcv_adv) even if we advertise a zero window. During the window while rcv_nxt is greather than rcv_adv, a few places would compute the remaining receive window via rcv_adv - rcv_nxt. However, this value was then (uint32_t)-1. On a 64 bit machine this could expand to a positive 2^32 - 1 when cast to a long. In particular, when calculating the receive window in tcp_output(), the result would be that the receive window was computed as 2^32 - 1 resulting in advertising a far larger window to the remote peer than actually existed. Fix various places that compute the remaining receive window to either assert that it is not negative (i.e. rcv_nxt <= rcv_adv), or treat the window as full if rcv_nxt is greather than rcv_adv. Modified: stable/7/sys/netinet/tcp_input.c stable/7/sys/netinet/tcp_output.c stable/7/sys/netinet/tcp_timewait.c Directory Properties: stable/7/sys/ (props changed) stable/7/sys/cddl/contrib/opensolaris/ (props changed) stable/7/sys/contrib/dev/acpica/ (props changed) stable/7/sys/contrib/pf/ (props changed) Modified: stable/7/sys/netinet/tcp_input.c ============================================================================== --- stable/7/sys/netinet/tcp_input.c Mon Jun 20 18:08:34 2011 (r223343) +++ stable/7/sys/netinet/tcp_input.c Mon Jun 20 18:08:52 2011 (r223344) @@ -1236,6 +1236,9 @@ tcp_do_segment(struct mbuf *m, struct tc win = sbspace(&so->so_rcv); if (win < 0) win = 0; + KASSERT(SEQ_GEQ(tp->rcv_adv, tp->rcv_nxt), + ("tcp_input negative window: tp %p rcv_nxt %u rcv_adv %u", tp, + tp->rcv_adv, tp->rcv_nxt)); tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt)); /* Reset receive buffer auto scaling when not in bulk receive mode. */ @@ -2288,7 +2291,10 @@ dodata: /* XXX */ * buffer size. * XXX: Unused. */ - len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt); + if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) + len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt); + else + len = so->so_rcv.sb_hiwat; #endif } else { m_freem(m); Modified: stable/7/sys/netinet/tcp_output.c ============================================================================== --- stable/7/sys/netinet/tcp_output.c Mon Jun 20 18:08:34 2011 (r223343) +++ stable/7/sys/netinet/tcp_output.c Mon Jun 20 18:08:52 2011 (r223344) @@ -557,15 +557,21 @@ after_sack_rexmit: * taking into account that we are limited by * TCP_MAXWIN << tp->rcv_scale. */ - long adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) - - (tp->rcv_adv - tp->rcv_nxt); + long adv; + int oldwin; + + adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale); + if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) { + oldwin = (tp->rcv_adv - tp->rcv_nxt); + adv -= oldwin; + } else + oldwin = 0; /* * If the new window size ends up being the same as the old * size when it is scaled, then don't force a window update. */ - if ((tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale == - (adv + tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale) + if (oldwin >> tp->rcv_scale == (adv + oldwin) >> tp->rcv_scale) goto dontupdate; if (adv >= (long) (2 * tp->t_maxseg)) goto send; @@ -935,7 +941,8 @@ send: if (recwin < (long)(so->so_rcv.sb_hiwat / 4) && recwin < (long)tp->t_maxseg) recwin = 0; - if (recwin < (long)(tp->rcv_adv - tp->rcv_nxt)) + if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) && + recwin < (long)(tp->rcv_adv - tp->rcv_nxt)) recwin = (long)(tp->rcv_adv - tp->rcv_nxt); if (recwin > (long)TCP_MAXWIN << tp->rcv_scale) recwin = (long)TCP_MAXWIN << tp->rcv_scale; @@ -1239,7 +1246,7 @@ out: * then remember the size of the advertised window. * Any pending ACK has now been sent. */ - if (recwin > 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv)) + if (recwin >= 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv)) tp->rcv_adv = tp->rcv_nxt + recwin; tp->last_ack_sent = tp->rcv_nxt; tp->t_flags &= ~(TF_ACKNOW | TF_DELACK); Modified: stable/7/sys/netinet/tcp_timewait.c ============================================================================== --- stable/7/sys/netinet/tcp_timewait.c Mon Jun 20 18:08:34 2011 (r223343) +++ stable/7/sys/netinet/tcp_timewait.c Mon Jun 20 18:08:52 2011 (r223344) @@ -210,6 +210,9 @@ tcp_twstart(struct tcpcb *tp) /* * Recover last window size sent. */ + KASSERT(SEQ_GEQ(tp->rcv_adv, tp->rcv_nxt), + ("tcp_twstart negative window: tp %p rcv_nxt %u rcv_adv %u", tp, + tp->rcv_adv, tp->rcv_nxt)); tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale; /*
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