[PATCH] tipc: Fix uninit-value access in __tipc_nl_bearer_enable()

[Shigeru Yoshida]

syzbot reported the following uninit-value access issue:

=====================================================
BUG: KMSAN: uninit-value in strscpy+0xc4/0x160
 strscpy+0xc4/0x160
 bearer_name_validate net/tipc/bearer.c:147 [inline]
 tipc_enable_bearer net/tipc/bearer.c:259 [inline]
 __tipc_nl_bearer_enable+0x634/0x2220 net/tipc/bearer.c:1043
 tipc_nl_bearer_enable+0x3c/0x70 net/tipc/bearer.c:1052
 genl_family_rcv_msg_doit net/netlink/genetlink.c:971 [inline]
 genl_family_rcv_msg net/netlink/genetlink.c:1051 [inline]
 genl_rcv_msg+0x11ec/0x1290 net/netlink/genetlink.c:1066
 netlink_rcv_skb+0x371/0x650 net/netlink/af_netlink.c:2545
 genl_rcv+0x40/0x60 net/netlink/genetlink.c:1075
 netlink_unicast_kernel net/netlink/af_netlink.c:1342 [inline]
 netlink_unicast+0xf47/0x1250 net/netlink/af_netlink.c:1368
 netlink_sendmsg+0x1238/0x13d0 net/netlink/af_netlink.c:1910
 sock_sendmsg_nosec net/socket.c:730 [inline]
 sock_sendmsg net/socket.c:753 [inline]
 ____sys_sendmsg+0x9c2/0xd60 net/socket.c:2540
 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2594
 __sys_sendmsg net/socket.c:2623 [inline]
 __do_sys_sendmsg net/socket.c:2632 [inline]
 __se_sys_sendmsg net/socket.c:2630 [inline]
 __x64_sys_sendmsg+0x307/0x490 net/socket.c:2630
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Uninit was created at:
 slab_post_alloc_hook+0x12f/0xb70 mm/slab.h:767
 slab_alloc_node mm/slub.c:3478 [inline]
 kmem_cache_alloc_node+0x577/0xa80 mm/slub.c:3523
 kmalloc_reserve+0x148/0x470 net/core/skbuff.c:559
 __alloc_skb+0x318/0x740 net/core/skbuff.c:644
 alloc_skb include/linux/skbuff.h:1286 [inline]
 netlink_alloc_large_skb net/netlink/af_netlink.c:1214 [inline]
 netlink_sendmsg+0xb34/0x13d0 net/netlink/af_netlink.c:1885
 sock_sendmsg_nosec net/socket.c:730 [inline]
 sock_sendmsg net/socket.c:753 [inline]
 ____sys_sendmsg+0x9c2/0xd60 net/socket.c:2540
 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2594
 __sys_sendmsg net/socket.c:2623 [inline]
 __do_sys_sendmsg net/socket.c:2632 [inline]
 __se_sys_sendmsg net/socket.c:2630 [inline]
 __x64_sys_sendmsg+0x307/0x490 net/socket.c:2630
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Bearer names must be null-terminated strings. If a bearer name which is not
null-terminated is passed through netlink, strcpy() and similar functions
can cause buffer overrun. This causes the above issue.

This patch fixes this issue by returning -EINVAL if a non-null-terminated
bearer name is passed.

Fixes: 0655f6a8635b ("tipc: add bearer disable/enable to new netlink api")
Reported-and-tested-by: syzbot+9425c47dccbcb4c17d51@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=9425c47dccbcb4c17d51
Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
---
 net/tipc/bearer.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/tipc/bearer.c b/net/tipc/bearer.c
index 2cde375477e3..62047d20e14d 100644
--- a/net/tipc/bearer.c
+++ b/net/tipc/bearer.c
@@ -1025,6 +1025,10 @@ int __tipc_nl_bearer_enable(struct sk_buff *skb, struct genl_info *info)
 
 	bearer = nla_data(attrs[TIPC_NLA_BEARER_NAME]);
 
+	if (bearer[strnlen(bearer,
+			   nla_len(attrs[TIPC_NLA_BEARER_NAME]))] != '\0')
+		return -EINVAL;
+
 	if (attrs[TIPC_NLA_BEARER_DOMAIN])
 		domain = nla_get_u32(attrs[TIPC_NLA_BEARER_DOMAIN]);
 
-- 
2.41.0