Date: Fri, 8 Dec 2006 10:36:46 +0000 (UTC) From: Luigi Rizzo <luigi@FreeBSD.org> To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/net if_ethersubr.c Message-ID: <200612081036.kB8AakMD029277@repoman.freebsd.org>
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luigi 2006-12-08 10:36:45 UTC
FreeBSD src repository
Modified files:
sys/net if_ethersubr.c
Log:
Fix an oscure bug triggered by a recent change in kern_socket.c.
The symptoms were that outgoing DHCP requests for diskless kernels
had the IP header corrupt. After long investigations, the source of
the problem was found in ether_output() - for SIMPLEX interfaces
and broadcast traffic, a copy of the packet is passed back to the kernel
through if_simloop(). However if_simloop() modifies the mbuf, while
the copy obtained through m_copym() is a readonly one.
The bug has been there forever, but it has been triggered only recently
by a change in sosend_dgram() which passed down mbufs with sufficient
space to prepend the header.
This fix is trivial - use m_dup() instead of m_copy() to create
the copy. As an alternative, we could try and modify if_simloop()
to play safely with readonly mbufs, but i don't think it is worthwhile
because 1) this is a relatively infrequent code path so we do not need
to worry too much about performance, and 2) the cost of doing an
extra m_pullup in if_simloop() is probably the same as doing the
copy of the cluster, anyways.
MFC after: 1 week
Revision Changes Path
1.221 +9 -1 src/sys/net/if_ethersubr.c
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