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pf: IPv6 fragments with malformed extension headers could be erroneously passed by pf or cause a panic

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We mistakenly used the extoff value from the last packet to patch the
next_header field. If a malicious host sends a chain of fragmented packets
where the first packet and the final packet have different lengths or number of
extension headers we'd patch the next_header at the wrong offset.
This can potentially lead to panics or rule bypasses.

Security:       CVE-2019-5597
Obtained from:  OpenBSD
Reported by:    Corentin Bayet, Nicolas Collignon, Luca Moro at Synacktiv
This commit is contained in:
Kristof Provost 2019-03-01 07:37:45 +00:00
parent b8da50d526
commit 6f4909de5f
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=344691
1 changed files with 2 additions and 2 deletions
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4
sys/netpfil/pf/pf_norm.c
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@ -836,11 +836,11 @@ pf_reassemble6(struct mbuf **m0, struct ip6_hdr *ip6, struct ip6_frag *fraghdr,
}
/* We have all the data. */
frent = TAILQ_FIRST(&frag->fr_queue);
KASSERT(frent != NULL, ("frent != NULL"));
extoff = frent->fe_extoff;
maxlen = frag->fr_maxlen;
frag_id = frag->fr_id;
frent = TAILQ_FIRST(&frag->fr_queue);
KASSERT(frent != NULL, ("frent != NULL"));
total = TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_off +
TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_len;
hdrlen = frent->fe_hdrlen - sizeof(struct ip6_frag);