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pf: Fix unaligned checksum updates

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The algorithm we use to update checksums only works correctly if the
updated data is aligned on 16-bit boundaries (relative to the start of
the packet).

Import the OpenBSD fix for this issue.

PR:		240416
Obtained from:	OpenBSD
MFC after:	1 week
Reviewed by:	tuexen (previous version)
Differential Revision:	https://reviews.freebsd.org/D27696
This commit is contained in:
Kristof Provost 2020-12-20 21:06:32 +01:00
parent 1622a49852
commit c3f69af03a
3 changed files with 89 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
sys/net/pfvar.h
View File

@ -330,6 +330,8 @@ extern struct sx pf_end_lock;
(neg) \
)
#define PF_ALGNMNT(off) (((off) % 2) == 0)
struct pf_rule_uid {
uid_t uid[2];
u_int8_t op;
@ -1735,6 +1737,10 @@ void pf_change_a(void *, u_int16_t *, u_int32_t, u_int8_t);
void pf_change_proto_a(struct mbuf *, void *, u_int16_t *, u_int32_t,
u_int8_t);
void pf_change_tcp_a(struct mbuf *, void *, u_int16_t *, u_int32_t);
void pf_patch_16_unaligned(struct mbuf *, u_int16_t *, void *, u_int16_t,
bool, u_int8_t);
void pf_patch_32_unaligned(struct mbuf *, u_int16_t *, void *, u_int32_t,
bool, u_int8_t);
void pf_send_deferred_syn(struct pf_state *);
int pf_match_addr(u_int8_t, struct pf_addr *, struct pf_addr *,
struct pf_addr *, sa_family_t);

79
sys/netpfil/pf/pf.c
View File

@ -288,6 +288,8 @@ static void pf_print_state_parts(struct pf_state *,
struct pf_state_key *, struct pf_state_key *);
static int pf_addr_wrap_neq(struct pf_addr_wrap *,
struct pf_addr_wrap *);
static void pf_patch_8(struct mbuf *, u_int16_t *, u_int8_t *, u_int8_t,
bool, u_int8_t);
static struct pf_state *pf_find_state(struct pfi_kif *,
struct pf_state_key_cmp *, u_int);
static int pf_src_connlimit(struct pf_state **);
@ -2084,16 +2086,60 @@ pf_addr_wrap_neq(struct pf_addr_wrap *aw1, struct pf_addr_wrap *aw2)
u_int16_t
pf_cksum_fixup(u_int16_t cksum, u_int16_t old, u_int16_t new, u_int8_t udp)
{
u_int32_t l;
u_int32_t x;
if (udp && !cksum)
return (0x0000);
l = cksum + old - new;
l = (l >> 16) + (l & 65535);
l = l & 65535;
if (udp && !l)
return (0xFFFF);
return (l);
x = cksum + old - new;
x = (x + (x >> 16)) & 0xffff;
/* optimise: eliminate a branch when not udp */
if (udp && cksum == 0x0000)
return cksum;
if (udp && x == 0x0000)
x = 0xffff;
return (u_int16_t)(x);
}
static void
pf_patch_8(struct mbuf *m, u_int16_t *cksum, u_int8_t *f, u_int8_t v, bool hi,
u_int8_t udp)
{
u_int16_t old = htons(hi ? (*f << 8) : *f);
u_int16_t new = htons(hi ? ( v << 8) : v);
if (*f == v)
return;
*f = v;
if (m->m_pkthdr.csum_flags & (CSUM_DELAY_DATA | CSUM_DELAY_DATA_IPV6))
return;
*cksum = pf_cksum_fixup(*cksum, old, new, udp);
}
void
pf_patch_16_unaligned(struct mbuf *m, u_int16_t *cksum, void *f, u_int16_t v,
bool hi, u_int8_t udp)
{
u_int8_t *fb = (u_int8_t *)f;
u_int8_t *vb = (u_int8_t *)&v;
pf_patch_8(m, cksum, fb++, *vb++, hi, udp);
pf_patch_8(m, cksum, fb++, *vb++, !hi, udp);
}
void
pf_patch_32_unaligned(struct mbuf *m, u_int16_t *cksum, void *f, u_int32_t v,
bool hi, u_int8_t udp)
{
u_int8_t *fb = (u_int8_t *)f;
u_int8_t *vb = (u_int8_t *)&v;
pf_patch_8(m, cksum, fb++, *vb++, hi, udp);
pf_patch_8(m, cksum, fb++, *vb++, !hi, udp);
pf_patch_8(m, cksum, fb++, *vb++, hi, udp);
pf_patch_8(m, cksum, fb++, *vb++, !hi, udp);
}
u_int16_t
@ -2319,6 +2365,7 @@ pf_modulate_sack(struct mbuf *m, int off, struct pf_pdesc *pd,
return 0;
while (hlen >= TCPOLEN_SACKLEN) {
size_t startoff = opt - opts;
olen = opt[1];
switch (*opt) {
case TCPOPT_EOL: /* FALLTHROUGH */
@ -2333,10 +2380,16 @@ pf_modulate_sack(struct mbuf *m, int off, struct pf_pdesc *pd,
for (i = 2; i + TCPOLEN_SACK <= olen;
i += TCPOLEN_SACK) {
memcpy(&sack, &opt[i], sizeof(sack));
pf_change_proto_a(m, &sack.start, &th->th_sum,
htonl(ntohl(sack.start) - dst->seqdiff), 0);
pf_change_proto_a(m, &sack.end, &th->th_sum,
htonl(ntohl(sack.end) - dst->seqdiff), 0);
pf_patch_32_unaligned(m,
&th->th_sum, &sack.start,
htonl(ntohl(sack.start) - dst->seqdiff),
PF_ALGNMNT(startoff),
0);
pf_patch_32_unaligned(m, &th->th_sum,
&sack.end,
htonl(ntohl(sack.end) - dst->seqdiff),
PF_ALGNMNT(startoff),
0);
memcpy(&opt[i], &sack, sizeof(sack));
}
copyback = 1;

23
sys/netpfil/pf/pf_norm.c
View File

@ -1517,6 +1517,7 @@ pf_normalize_tcp_stateful(struct mbuf *m, int off, struct pf_pdesc *pd,
u_int8_t *opt;
int copyback = 0;
int got_ts = 0;
size_t startoff;
KASSERT((src->scrub || dst->scrub),
("%s: src->scrub && dst->scrub!", __func__));
@ -1560,6 +1561,7 @@ pf_normalize_tcp_stateful(struct mbuf *m, int off, struct pf_pdesc *pd,
opt = hdr + sizeof(struct tcphdr);
hlen = (th->th_off << 2) - sizeof(struct tcphdr);
while (hlen >= TCPOLEN_TIMESTAMP) {
startoff = opt - (hdr + sizeof(struct tcphdr));
switch (*opt) {
case TCPOPT_EOL: /* FALLTHROUGH */
case TCPOPT_NOP:
@ -1589,10 +1591,12 @@ pf_normalize_tcp_stateful(struct mbuf *m, int off, struct pf_pdesc *pd,
(src->scrub->pfss_flags &
PFSS_TIMESTAMP)) {
tsval = ntohl(tsval);
pf_change_proto_a(m, &opt[2],
pf_patch_32_unaligned(m,
&th->th_sum,
&opt[2],
htonl(tsval +
src->scrub->pfss_ts_mod),
PF_ALGNMNT(startoff),
0);
copyback = 1;
}
@ -1605,8 +1609,11 @@ pf_normalize_tcp_stateful(struct mbuf *m, int off, struct pf_pdesc *pd,
PFSS_TIMESTAMP)) {
tsecr = ntohl(tsecr)
- dst->scrub->pfss_ts_mod;
pf_change_proto_a(m, &opt[6],
&th->th_sum, htonl(tsecr),
pf_patch_32_unaligned(m,
&th->th_sum,
&opt[6],
htonl(tsecr),
PF_ALGNMNT(startoff),
0);
copyback = 1;
}
@ -1903,6 +1910,7 @@ pf_normalize_tcpopt(struct pf_rule *r, struct mbuf *m, struct tcphdr *th,
int rewrite = 0;
u_char opts[TCP_MAXOLEN];
u_char *optp = opts;
size_t startoff;
thoff = th->th_off << 2;
cnt = thoff - sizeof(struct tcphdr);
@ -1912,6 +1920,7 @@ pf_normalize_tcpopt(struct pf_rule *r, struct mbuf *m, struct tcphdr *th,
return (rewrite);
for (; cnt > 0; cnt -= optlen, optp += optlen) {
startoff = optp - opts;
opt = optp[0];
if (opt == TCPOPT_EOL)
break;
@ -1928,9 +1937,11 @@ pf_normalize_tcpopt(struct pf_rule *r, struct mbuf *m, struct tcphdr *th,
case TCPOPT_MAXSEG:
mss = (u_int16_t *)(optp + 2);
if ((ntohs(*mss)) > r->max_mss) {
th->th_sum = pf_proto_cksum_fixup(m,
th->th_sum, *mss, htons(r->max_mss), 0);
*mss = htons(r->max_mss);
pf_patch_16_unaligned(m,
&th->th_sum,
mss, htons(r->max_mss),
PF_ALGNMNT(startoff),
0);
rewrite = 1;
}
break;