[PATCH v2 net] net/tcp: fix possible out-of-bounds reads in tcp_hash_fail()

[Eric Dumazet <edumazet@google.com>]

syzbot managed to trigger a fault by sending TCP packets
with all flags being set.

v2:
 - While fixing this bug, add PSH flag handling and represent
   flags the way tcpdump does : [S], [S.], [P.]
 - Print 4-tuples more consistently between families.

BUG: KASAN: stack-out-of-bounds in string_nocheck lib/vsprintf.c:645 [inline]
BUG: KASAN: stack-out-of-bounds in string+0x394/0x3d0 lib/vsprintf.c:727
Read of size 1 at addr ffffc9000397f3f5 by task syz-executor299/5039

CPU: 1 PID: 5039 Comm: syz-executor299 Not tainted 6.6.0-rc7-syzkaller-02075-g55c900477f5b #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xc4/0x620 mm/kasan/report.c:475
kasan_report+0xda/0x110 mm/kasan/report.c:588
string_nocheck lib/vsprintf.c:645 [inline]
string+0x394/0x3d0 lib/vsprintf.c:727
vsnprintf+0xc5f/0x1870 lib/vsprintf.c:2818
vprintk_store+0x3a0/0xb80 kernel/printk/printk.c:2191
vprintk_emit+0x14c/0x5f0 kernel/printk/printk.c:2288
vprintk+0x7b/0x90 kernel/printk/printk_safe.c:45
_printk+0xc8/0x100 kernel/printk/printk.c:2332
tcp_inbound_hash.constprop.0+0xdb2/0x10d0 include/net/tcp.h:2760
tcp_v6_rcv+0x2b31/0x34d0 net/ipv6/tcp_ipv6.c:1882
ip6_protocol_deliver_rcu+0x33b/0x13d0 net/ipv6/ip6_input.c:438
ip6_input_finish+0x14f/0x2f0 net/ipv6/ip6_input.c:483
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ip6_input+0xce/0x440 net/ipv6/ip6_input.c:492
dst_input include/net/dst.h:461 [inline]
ip6_rcv_finish net/ipv6/ip6_input.c:79 [inline]
NF_HOOK include/linux/netfilter.h:314 [inline]
NF_HOOK include/linux/netfilter.h:308 [inline]
ipv6_rcv+0x563/0x720 net/ipv6/ip6_input.c:310
__netif_receive_skb_one_core+0x115/0x180 net/core/dev.c:5527
__netif_receive_skb+0x1f/0x1b0 net/core/dev.c:5641
netif_receive_skb_internal net/core/dev.c:5727 [inline]
netif_receive_skb+0x133/0x700 net/core/dev.c:5786
tun_rx_batched+0x429/0x780 drivers/net/tun.c:1579
tun_get_user+0x29e7/0x3bc0 drivers/net/tun.c:2002
tun_chr_write_iter+0xe8/0x210 drivers/net/tun.c:2048
call_write_iter include/linux/fs.h:1956 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x650/0xe40 fs/read_write.c:584
ksys_write+0x12f/0x250 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: 2717b5adea9e ("net/tcp: Add tcp_hash_fail() ratelimited logs")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Dmitry Safonov <dima@arista.com>
Cc: Francesco Ruggeri <fruggeri@arista.com>
Cc: David Ahern <dsahern@kernel.org>
---
 include/net/tcp_ao.h | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h
index a375a171ef3cb37ab1d8246c72c6a3e83f5c9184..b56be10838f09a2cb56ab511242d2b583eb4c33b 100644
--- a/include/net/tcp_ao.h
+++ b/include/net/tcp_ao.h
@@ -124,7 +124,7 @@ struct tcp_ao_info {
 #define tcp_hash_fail(msg, family, skb, fmt, ...)			\
 do {									\
 	const struct tcphdr *th = tcp_hdr(skb);				\
-	char hdr_flags[5] = {};						\
+	char hdr_flags[6];						\
 	char *f = hdr_flags;						\
 									\
 	if (th->fin)							\
@@ -133,17 +133,18 @@ do {									\
 		*f++ = 'S';						\
 	if (th->rst)							\
 		*f++ = 'R';						\
+	if (th->psh)							\
+		*f++ = 'P';						\
 	if (th->ack)							\
-		*f++ = 'A';						\
-	if (f != hdr_flags)						\
-		*f = ' ';						\
+		*f++ = '.';						\
+	*f = 0;								\
 	if ((family) == AF_INET) {					\
-		net_info_ratelimited("%s for (%pI4, %d)->(%pI4, %d) %s" fmt "\n", \
+		net_info_ratelimited("%s for %pI4.%d->%pI4.%d [%s] " fmt "\n", \
 				msg, &ip_hdr(skb)->saddr, ntohs(th->source), \
 				&ip_hdr(skb)->daddr, ntohs(th->dest),	\
 				hdr_flags, ##__VA_ARGS__);		\
 	} else {							\
-		net_info_ratelimited("%s for [%pI6c]:%u->[%pI6c]:%u %s" fmt "\n", \
+		net_info_ratelimited("%s for [%pI6c].%d->[%pI6c].%d [%s]" fmt "\n", \
 				msg, &ipv6_hdr(skb)->saddr, ntohs(th->source), \
 				&ipv6_hdr(skb)->daddr, ntohs(th->dest),	\
 				hdr_flags, ##__VA_ARGS__);		\
-- 
2.42.0.820.g83a721a137-goog