[PATCH net] tcp: fix TCP_REPAIR_QUEUE bound checking

[PATCH net] tcp: fix TCP_REPAIR_QUEUE bound checking

[Eric Dumazet]

syzbot is able to produce a nasty WARN_ON() in tcp_verify_left_out()
with following C-repro :

socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
setsockopt(3, SOL_TCP, TCP_REPAIR, [1], 4) = 0
setsockopt(3, SOL_TCP, TCP_REPAIR_QUEUE, [-1], 4) = 0
bind(3, {sa_family=AF_INET, sin_port=htons(20002), sin_addr=inet_addr("0.0.0.0")}, 16) = 0
sendto(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
	1242, MSG_FASTOPEN, {sa_family=AF_INET, sin_port=htons(20002), sin_addr=inet_addr("127.0.0.1")}, 16) = 1242
setsockopt(3, SOL_TCP, TCP_REPAIR_WINDOW, "\4\0\0@+\205\0\0\377\377\0\0\377\377\377\177\0\0\0\0", 20) = 0
writev(3, [{"\270", 1}], 1)             = 1
setsockopt(3, SOL_TCP, TCP_REPAIR_OPTIONS, "\10\0\0\0\0\0\0\0\0\0\0\0|\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 386) = 0
writev(3, [{"\210v\r[\226\320t\231qwQ\204\264l\254\t\1\20\245\214p\350H\223\254;\\\37\345\307p$"..., 3144}], 1) = 3144

The 3rd system call looks odd :
setsockopt(3, SOL_TCP, TCP_REPAIR_QUEUE, [-1], 4) = 0

This patch makes sure bound checking is using an unsigned compare.

Fixes: ee9952831cfd ("tcp: Initial repair mode")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
---
 net/ipv4/tcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 4b18ad41d4df354b151ef2a05e771cce48dcb5b7..44be7f43455e4aefde8db61e2d941a69abcc642a 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2674,7 +2674,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
 	case TCP_REPAIR_QUEUE:
 		if (!tp->repair)
 			err = -EPERM;
-		else if (val < TCP_QUEUES_NR)
+		else if ((unsigned int)val < TCP_QUEUES_NR)
 			tp->repair_queue = val;
 		else
 			err = -EINVAL;
-- 
2.17.0.441.gb46fe60e1d-goog

Re: [PATCH net] tcp: fix TCP_REPAIR_QUEUE bound checking

[David Miller]

From: Eric Dumazet <edumazet@google.com>
Date: Sun, 29 Apr 2018 18:55:20 -0700

> syzbot is able to produce a nasty WARN_ON() in tcp_verify_left_out()
> with following C-repro :
> 
> socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
> setsockopt(3, SOL_TCP, TCP_REPAIR, [1], 4) = 0
> setsockopt(3, SOL_TCP, TCP_REPAIR_QUEUE, [-1], 4) = 0
> bind(3, {sa_family=AF_INET, sin_port=htons(20002), sin_addr=inet_addr("0.0.0.0")}, 16) = 0
> sendto(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
> 	1242, MSG_FASTOPEN, {sa_family=AF_INET, sin_port=htons(20002), sin_addr=inet_addr("127.0.0.1")}, 16) = 1242
> setsockopt(3, SOL_TCP, TCP_REPAIR_WINDOW, "\4\0\0@+\205\0\0\377\377\0\0\377\377\377\177\0\0\0\0", 20) = 0
> writev(3, [{"\270", 1}], 1)             = 1
> setsockopt(3, SOL_TCP, TCP_REPAIR_OPTIONS, "\10\0\0\0\0\0\0\0\0\0\0\0|\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 386) = 0
> writev(3, [{"\210v\r[\226\320t\231qwQ\204\264l\254\t\1\20\245\214p\350H\223\254;\\\37\345\307p$"..., 3144}], 1) = 3144
> 
> The 3rd system call looks odd :
> setsockopt(3, SOL_TCP, TCP_REPAIR_QUEUE, [-1], 4) = 0
> 
> This patch makes sure bound checking is using an unsigned compare.
> 
> Fixes: ee9952831cfd ("tcp: Initial repair mode")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Reported-by: syzbot <syzkaller@googlegroups.com>

Ouch.

Applied and queued up for -stable, thanks Eric.