[PATCH net v2] tipc: Fix uninit-value access in tipc_nl_node_reset_link_stats()

[PATCH net v2] tipc: Fix uninit-value access in tipc_nl_node_reset_link_stats()

[Shigeru Yoshida]

syzbot reported the following uninit-value access issue:

=====================================================
BUG: KMSAN: uninit-value in strlen lib/string.c:418 [inline]
BUG: KMSAN: uninit-value in strstr+0xb8/0x2f0 lib/string.c:756
 strlen lib/string.c:418 [inline]
 strstr+0xb8/0x2f0 lib/string.c:756
 tipc_nl_node_reset_link_stats+0x3ea/0xb50 net/tipc/node.c:2595
 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:2541
 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2595
 __sys_sendmsg net/socket.c:2624 [inline]
 __do_sys_sendmsg net/socket.c:2633 [inline]
 __se_sys_sendmsg net/socket.c:2631 [inline]
 __x64_sys_sendmsg+0x307/0x490 net/socket.c:2631
 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+0x13d/0x4a0 net/core/skbuff.c:559
 __alloc_skb+0x318/0x740 net/core/skbuff.c:650
 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:2541
 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2595
 __sys_sendmsg net/socket.c:2624 [inline]
 __do_sys_sendmsg net/socket.c:2633 [inline]
 __se_sys_sendmsg net/socket.c:2631 [inline]
 __x64_sys_sendmsg+0x307/0x490 net/socket.c:2631
 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

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

This patch resolves the issue by using nla_strscpy() to ensure the link
name is null-terminated.

Fixes: ae36342b50a9 ("tipc: add link stat reset to new netlink api")
Reported-and-tested-by: syzbot+5138ca807af9d2b42574@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5138ca807af9d2b42574
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
---
v1->v2:
- Use nla_strscpy()
- Fix similar bugs in other functions other than syzbot reported
---
 net/tipc/node.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/net/tipc/node.c b/net/tipc/node.c
index 3105abe97bb9..2121908e56c1 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -2419,7 +2419,7 @@ int tipc_nl_node_set_link(struct sk_buff *skb, struct genl_info *info)
 	int err;
 	int res = 0;
 	int bearer_id;
-	char *name;
+	char name[TIPC_MAX_LINK_NAME];
 	struct tipc_link *link;
 	struct tipc_node *node;
 	struct sk_buff_head xmitq;
@@ -2440,7 +2440,7 @@ int tipc_nl_node_set_link(struct sk_buff *skb, struct genl_info *info)
 	if (!attrs[TIPC_NLA_LINK_NAME])
 		return -EINVAL;
 
-	name = nla_data(attrs[TIPC_NLA_LINK_NAME]);
+	nla_strscpy(name, attrs[TIPC_NLA_LINK_NAME], TIPC_MAX_LINK_NAME);
 
 	if (strcmp(name, tipc_bclink_name) == 0)
 		return tipc_nl_bc_link_set(net, attrs);
@@ -2500,7 +2500,7 @@ int tipc_nl_node_get_link(struct sk_buff *skb, struct genl_info *info)
 	struct net *net = genl_info_net(info);
 	struct nlattr *attrs[TIPC_NLA_LINK_MAX + 1];
 	struct tipc_nl_msg msg;
-	char *name;
+	char name[TIPC_MAX_LINK_NAME];
 	int err;
 
 	msg.portid = info->snd_portid;
@@ -2518,7 +2518,7 @@ int tipc_nl_node_get_link(struct sk_buff *skb, struct genl_info *info)
 	if (!attrs[TIPC_NLA_LINK_NAME])
 		return -EINVAL;
 
-	name = nla_data(attrs[TIPC_NLA_LINK_NAME]);
+	nla_strscpy(name, attrs[TIPC_NLA_LINK_NAME], TIPC_MAX_LINK_NAME);
 
 	msg.skb = nlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
 	if (!msg.skb)
@@ -2563,7 +2563,7 @@ int tipc_nl_node_get_link(struct sk_buff *skb, struct genl_info *info)
 int tipc_nl_node_reset_link_stats(struct sk_buff *skb, struct genl_info *info)
 {
 	int err;
-	char *link_name;
+	char link_name[TIPC_MAX_LINK_NAME];
 	unsigned int bearer_id;
 	struct tipc_link *link;
 	struct tipc_node *node;
@@ -2584,7 +2584,7 @@ int tipc_nl_node_reset_link_stats(struct sk_buff *skb, struct genl_info *info)
 	if (!attrs[TIPC_NLA_LINK_NAME])
 		return -EINVAL;
 
-	link_name = nla_data(attrs[TIPC_NLA_LINK_NAME]);
+	nla_strscpy(link_name, attrs[TIPC_NLA_LINK_NAME], TIPC_MAX_LINK_NAME);
 
 	err = -EINVAL;
 	if (!strcmp(link_name, tipc_bclink_name)) {
-- 
2.41.0

Re: [PATCH net v2] tipc: Fix uninit-value access in tipc_nl_node_reset_link_stats()

[Jakub Kicinski]

On Sat, 21 Oct 2023 01:34:15 +0900 Shigeru Yoshida wrote:
> Link names must be null-terminated strings. If a link name which is not
> null-terminated is passed through netlink, strstr() and similar functions
> can cause buffer overrun. This causes the above issue.

If strings need to be null-terminated you should switch the policy here
https://elixir.bootlin.com/linux/v6.6-rc6/source/net/tipc/netlink.c#L91
from NLA_STRING to NLA_NUL_STRING, no?
-- 
pw-bot: cr

Re: [PATCH net v2] tipc: Fix uninit-value access in tipc_nl_node_reset_link_stats()

[Shigeru Yoshida]

On Mon, 23 Oct 2023 15:53:14 -0700, Jakub Kicinski wrote:
> On Sat, 21 Oct 2023 01:34:15 +0900 Shigeru Yoshida wrote:
>> Link names must be null-terminated strings. If a link name which is not
>> null-terminated is passed through netlink, strstr() and similar functions
>> can cause buffer overrun. This causes the above issue.
> 
> If strings need to be null-terminated you should switch the policy here
> https://elixir.bootlin.com/linux/v6.6-rc6/source/net/tipc/netlink.c#L91
> from NLA_STRING to NLA_NUL_STRING, no?

Thank you so much for the feedback. As I'm not so familiar with
Netlink, I'll study NLA_NUL_STRING a bit more and make an updated
patch.

Thanks,
Shigeru

> -- 
> pw-bot: cr
>