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Add some additional length checks to the IPv4 fragmentation code.

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Specifically, block 0-length fragments, even when the MF bit is clear.
Also, ensure that every fragment with the MF bit clear ends at the same
offset and that no subsequently-received fragments exceed that offset.

Reviewed by:	glebius, markj
MFC after:	3 days
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D17922
This commit is contained in:
Jonathan T. Looney 2018-11-16 18:32:48 +00:00
parent 2c054ce924
commit 2157f3c36a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=340483
2 changed files with 34 additions and 12 deletions
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45
sys/netinet/ip_reass.c
View File

@ -211,19 +211,21 @@ ip_reass(struct mbuf *m)
* convert offset of this to bytes.
*/
ip->ip_len = htons(ntohs(ip->ip_len) - hlen);
if (ip->ip_off & htons(IP_MF)) {
/*
* Make sure that fragments have a data length
* that's a non-zero multiple of 8 bytes.
*/
if (ip->ip_len == htons(0) || (ntohs(ip->ip_len) & 0x7) != 0) {
IPSTAT_INC(ips_toosmall); /* XXX */
IPSTAT_INC(ips_fragdropped);
m_freem(m);
return (NULL);
}
/*
* Make sure that fragments have a data length
* that's a non-zero multiple of 8 bytes, unless
* this is the last fragment.
*/
if (ip->ip_len == htons(0) ||
((ip->ip_off & htons(IP_MF)) && (ntohs(ip->ip_len) & 0x7) != 0)) {
IPSTAT_INC(ips_toosmall); /* XXX */
IPSTAT_INC(ips_fragdropped);
m_freem(m);
return (NULL);
}
if (ip->ip_off & htons(IP_MF))
m->m_flags |= M_IP_FRAG;
} else
else
m->m_flags &= ~M_IP_FRAG;
ip->ip_off = htons(ntohs(ip->ip_off) << 3);
@ -301,9 +303,28 @@ ip_reass(struct mbuf *m)
fp->ipq_src = ip->ip_src;
fp->ipq_dst = ip->ip_dst;
fp->ipq_frags = m;
if (m->m_flags & M_IP_FRAG)
fp->ipq_maxoff = -1;
else
fp->ipq_maxoff = ntohs(ip->ip_off) + ntohs(ip->ip_len);
m->m_nextpkt = NULL;
goto done;
} else {
/*
* If we already saw the last fragment, make sure
* this fragment's offset looks sane. Otherwise, if
* this is the last fragment, record its endpoint.
*/
if (fp->ipq_maxoff > 0) {
i = ntohs(ip->ip_off) + ntohs(ip->ip_len);
if (((m->m_flags & M_IP_FRAG) && i >= fp->ipq_maxoff) ||
((m->m_flags & M_IP_FRAG) == 0 &&
i != fp->ipq_maxoff)) {
fp = NULL;
goto dropfrag;
}
} else if ((m->m_flags & M_IP_FRAG) == 0)
fp->ipq_maxoff = ntohs(ip->ip_off) + ntohs(ip->ip_len);
fp->ipq_nfrags++;
atomic_add_int(&nfrags, 1);
#ifdef MAC

1
sys/netinet/ip_var.h
View File

@ -61,6 +61,7 @@ struct ipq {
u_char ipq_ttl; /* time for reass q to live */
u_char ipq_p; /* protocol of this fragment */
u_short ipq_id; /* sequence id for reassembly */
int ipq_maxoff; /* total length of packet */
struct mbuf *ipq_frags; /* to ip headers of fragments */
struct in_addr ipq_src,ipq_dst;
u_char ipq_nfrags; /* # frags in this packet */