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Avoid buffer underwrite in icmp_error

Description

Avoid buffer underwrite in icmp_error

icmp_error allocates either an mbuf (with pkthdr) or a cluster depending
on the size of data to be quoted in the ICMP reply, but the calculation
failed to account for the additional padding that m_align may apply.

Include the ip header in the size passed to m_align. On 64-bit archs
this will have the net effect of moving everything 4 bytes later in the
mbuf or cluster. This will result in slightly pessimal alignment for
the ICMP data copy.

Also add an assertion that we do not move m_data before the beginning of
the mbuf or cluster.

Reported by: A reddit user
Reviewed by: bz, jtl
MFC after: 3 days
Security: CVE-2018-17156
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D17909

Details

Committed
emasteThu, Nov 8, 8:17 PM
Reviewer
bz
Differential Revision
D17909: Avoid buffer underwrite in icmp_error
Parents
rS340259: MFC r340181, r340185:
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