possible bug in the sbappendrecord_locked()? (Was: Re: core
dump with bluetooth device)
Maksim Yevmenkin
maksim.yevmenkin at gmail.com
Fri Apr 17 15:55:09 UTC 2009
On Thu, Apr 16, 2009 at 9:48 PM, pluknet <pluknet at gmail.com> wrote:
> Sorry for top-posting.
>
> This is a fairly old bug.
> See my investigation
> http://lists.freebsd.org/pipermail/freebsd-net/2008-August/019345.html
ahh, i see. thanks for the pointer. please read below.
>>>>> <alexbestms at math.uni-muenster.de> wrote:
>>>>>> hi there,
>>>>>>
>>>>>> i'm running r191076M. when i try to send files from my mobile phone to my
>>>>>> computer via bt the core dumps. here's a backtrace:
>>>>>>
>>>>>> Unread portion of the kernel message buffer:
>>>>>> sblastmbufchk: sb_mb 0xc8d54d00 sb_mbtail 0 last 0xc8d54d00
>>>>>> packet tree:
>>>>>> 0xc8d54d00
>>>>>> panic: sblastmbufchk from /usr/src/sys/kern/uipc_sockbuf.c:797
>>>>>> cpuid = 0
>>>>>
>>>>> are you, by change, have "options SOCKBUF_DEBUG" in your kernel?
>>>>
>>>> ok, there is something strange going on in the
>>>> sbappendrecord_locked(). consider the following initial conditions:
>>>>
>>>> 1) sockbuf sb is empty, i.e. sb_mb == sb_mbtail == sb_lastrecord == NULL
>>>>
>>>> 2) sbappendrecord_locked() is given mbuf m0 with has exactly one mbuf,
>>>> i.e. m0->m_next == NULL
>>>>
>>>> so
>>>>
>>>> void
>>>> sbappendrecord_locked(struct sockbuf *sb, struct mbuf *m0)
>>>> {
>>>> struct mbuf *m;
>>>>
>>>> SOCKBUF_LOCK_ASSERT(sb);
>>>>
>>>> if (m0 == 0)
>>>> return;
>>>> m = sb->sb_mb;
>>>>
>>>> if (m)
>>>> while (m->m_nextpkt)
>>>> m = m->m_nextpkt;
>>>>
>>>> --> m is still NULL at this point
>>>>
>>>> /*
>>>> * Put the first mbuf on the queue. Note this permits zero length
>>>> * records.
>>>> */
>>>> sballoc(sb, m0);
>>>> SBLASTRECORDCHK(sb);
>>>>
>>>> --> passed successfully, because sb_mb == sb_lastrecord == NULL (i.e.
>>>> sockbuf is empty)
>>>>
>>>> SBLINKRECORD(sb, m0);
>>>>
>>>> --> at this point sb_mb == sb_lastrecord == m0, _but_ sb_mtail == NULL
>>>>
>>>> if (m)
>>>> m->m_nextpkt = m0;
>>>> else
>>>> sb->sb_mb = m0;
>>>>
>>>> --> not sure about those lines above, didn't SBLINKRECORD(sb, m0) take
>>>> care of it already?
>>>> --> in any case, still, sb_mb == sb_lastrecord == m0 _and_ still
>>>> sb_mtail == NULL
>>>>
>>>> m = m0->m_next;
>>>> m0->m_next = 0;
>>>>
>>>> --> m is still NULL here
>>>>
>>>> if (m && (m0->m_flags & M_EOR)) {
>>>> m0->m_flags &= ~M_EOR;
>>>> m->m_flags |= M_EOR;
>>>> }
>>>>
>>>> --> sbcompress() is called with m == NULL, which is triggers the panic
>>>> (read below)
>>>>
>>>> sbcompress(sb, m, m0);
>>>> }
>>>>
>>>> ===========
>>>>
>>>> void
>>>> sbcompress(struct sockbuf *sb, struct mbuf *m, struct mbuf *n)
>>>> {
>>>> int eor = 0;
>>>> struct mbuf *o;
>>>>
>>>> SOCKBUF_LOCK_ASSERT(sb);
>>>>
>>>> while (m) {
>>>>
>>>> --> lots of code that never gets executed because m == NULL
>>>>
>>>> }
>>>> if (eor) {
>>>> KASSERT(n != NULL, ("sbcompress: eor && n == NULL"));
>>>> n->m_flags |= eor;
>>>> }
>>>>
>>>> --> this where panic happens, because sb_mbtail is still NULL, but
>>>> sockbuf now contains exactly one record
>>>>
>>>> SBLASTMBUFCHK(sb);
>>>> }
>>>>
>>>> so, it looks like, sbcompress() should only be called when m != NULL.
>>>> also, when m == NULL, m0 should be marked as EOR.
>>>
>>> actually, no, EOR should be set (or not set already).
>>>
>>>> comments anyone?
ok, this is completely untested, so be warned :) would something like
the following work? am i missing something?
> svn diff
Index: uipc_sockbuf.c
===================================================================
--- uipc_sockbuf.c (revision 191012)
+++ uipc_sockbuf.c (working copy)
@@ -577,10 +577,6 @@
if (m0 == 0)
return;
- m = sb->sb_mb;
- if (m)
- while (m->m_nextpkt)
- m = m->m_nextpkt;
/*
* Put the first mbuf on the queue. Note this permits zero length
* records.
@@ -588,17 +584,17 @@
sballoc(sb, m0);
SBLASTRECORDCHK(sb);
SBLINKRECORD(sb, m0);
- if (m)
- m->m_nextpkt = m0;
- else
- sb->sb_mb = m0;
+ sb->sb_mbtail = m0;
m = m0->m_next;
m0->m_next = 0;
- if (m && (m0->m_flags & M_EOR)) {
- m0->m_flags &= ~M_EOR;
- m->m_flags |= M_EOR;
+ if (m != NULL) {
+ if (m0->m_flags & M_EOR) {
+ m0->m_flags &= ~M_EOR;
+ m->m_flags |= M_EOR;
+ }
+
+ sbcompress(sb, m, m0);
}
- sbcompress(sb, m, m0);
}
/*
==
thanks,
max
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