[PATCH net] net/handshake: fix null-ptr-deref in handshake_nl_done_doit()

[PATCH net] net/handshake: fix null-ptr-deref in handshake_nl_done_doit()

[Eric Dumazet]

We should not call trace_handshake_cmd_done_err() if socket lookup has failed.

Also we should call trace_handshake_cmd_done_err() before releasing the file,
otherwise dereferencing sock->sk can return garbage.

This also reverts 7afc6d0a107f ("net/handshake: Fix uninitialized local variable")

Unable to handle kernel paging request at virtual address dfff800000000003
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
Mem abort info:
ESR = 0x0000000096000005
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x05: level 1 translation fault
Data abort info:
ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
CM = 0, WnR = 0, TnD = 0, TagAccess = 0
GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[dfff800000000003] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 5986 Comm: syz-executor292 Not tainted 6.5.0-rc7-syzkaller-gfe4469582053 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : handshake_nl_done_doit+0x198/0x9c8 net/handshake/netlink.c:193
lr : handshake_nl_done_doit+0x180/0x9c8
sp : ffff800096e37180
x29: ffff800096e37200 x28: 1ffff00012dc6e34 x27: dfff800000000000
x26: ffff800096e373d0 x25: 0000000000000000 x24: 00000000ffffffa8
x23: ffff800096e373f0 x22: 1ffff00012dc6e38 x21: 0000000000000000
x20: ffff800096e371c0 x19: 0000000000000018 x18: 0000000000000000
x17: 0000000000000000 x16: ffff800080516cc4 x15: 0000000000000001
x14: 1fffe0001b14aa3b x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000003
x8 : 0000000000000003 x7 : ffff800080afe47c x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff800080a88078
x2 : 0000000000000001 x1 : 00000000ffffffa8 x0 : 0000000000000000
Call trace:
handshake_nl_done_doit+0x198/0x9c8 net/handshake/netlink.c:193
genl_family_rcv_msg_doit net/netlink/genetlink.c:970 [inline]
genl_family_rcv_msg net/netlink/genetlink.c:1050 [inline]
genl_rcv_msg+0x96c/0xc50 net/netlink/genetlink.c:1067
netlink_rcv_skb+0x214/0x3c4 net/netlink/af_netlink.c:2549
genl_rcv+0x38/0x50 net/netlink/genetlink.c:1078
netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline]
netlink_unicast+0x660/0x8d4 net/netlink/af_netlink.c:1365
netlink_sendmsg+0x834/0xb18 net/netlink/af_netlink.c:1914
sock_sendmsg_nosec net/socket.c:725 [inline]
sock_sendmsg net/socket.c:748 [inline]
____sys_sendmsg+0x56c/0x840 net/socket.c:2494
___sys_sendmsg net/socket.c:2548 [inline]
__sys_sendmsg+0x26c/0x33c net/socket.c:2577
__do_sys_sendmsg net/socket.c:2586 [inline]
__se_sys_sendmsg net/socket.c:2584 [inline]
__arm64_sys_sendmsg+0x80/0x94 net/socket.c:2584
__invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:51
el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:136
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:155
el0_svc+0x58/0x16c arch/arm64/kernel/entry-common.c:678
el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:696
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:591
Code: 12800108 b90043e8 910062b3 d343fe68 (387b6908)

Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for handling handshake requests")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
---
 net/handshake/netlink.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/net/handshake/netlink.c b/net/handshake/netlink.c
index 1086653e1fada1724f98ccbc81fbcf7741ef9bc9..bfc8d6cf795bccd063dbdf1f5319cfa85ddbb8be 100644
--- a/net/handshake/netlink.c
+++ b/net/handshake/netlink.c
@@ -158,25 +158,23 @@ int handshake_nl_done_doit(struct sk_buff *skb, struct genl_info *info)
 {
 	struct net *net = sock_net(skb->sk);
 	struct handshake_req *req = NULL;
-	struct socket *sock = NULL;
+	struct socket *sock;
 	int fd, status, err;
 
 	if (GENL_REQ_ATTR_CHECK(info, HANDSHAKE_A_DONE_SOCKFD))
 		return -EINVAL;
 	fd = nla_get_u32(info->attrs[HANDSHAKE_A_DONE_SOCKFD]);
 
-	err = 0;
 	sock = sockfd_lookup(fd, &err);
-	if (err) {
-		err = -EBADF;
-		goto out_status;
-	}
+	if (!sock)
+		return err;
 
 	req = handshake_req_hash_lookup(sock->sk);
 	if (!req) {
 		err = -EBUSY;
+		trace_handshake_cmd_done_err(net, req, sock->sk, err);
 		fput(sock->file);
-		goto out_status;
+		return err;
 	}
 
 	trace_handshake_cmd_done(net, req, sock->sk, fd);
@@ -188,10 +186,6 @@ int handshake_nl_done_doit(struct sk_buff *skb, struct genl_info *info)
 	handshake_complete(req, status, info);
 	fput(sock->file);
 	return 0;
-
-out_status:
-	trace_handshake_cmd_done_err(net, req, sock->sk, err);
-	return err;
 }
 
 static unsigned int handshake_net_id;
-- 
2.42.0.rc1.204.g551eb34607-goog

Re: [PATCH net] net/handshake: fix null-ptr-deref in handshake_nl_done_doit()

[Paolo Abeni]

On Mon, 2023-08-28 at 09:13 +0000, Eric Dumazet wrote:
> We should not call trace_handshake_cmd_done_err() if socket lookup has failed.

I think Chuck would like to have a tracepoint for all the possible
handshake_nl_done_doit() failures, but guess that could be added later
on net-next, possibly refactoring the arguments list (e.g. adding an
explicit fd arg, and passing explicitly a NULL sk).

> Also we should call trace_handshake_cmd_done_err() before releasing the file,
> otherwise dereferencing sock->sk can return garbage.
> 
> This also reverts 7afc6d0a107f ("net/handshake: Fix uninitialized local variable")

I can be low on coffee, but

	struct handshake_req *req = NULL;

is still there after this patch ?!?

Cheers,

Paolo

Re: [PATCH net] net/handshake: fix null-ptr-deref in handshake_nl_done_doit()

[Eric Dumazet]

On Thu, Aug 31, 2023 at 9:55 AM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Mon, 2023-08-28 at 09:13 +0000, Eric Dumazet wrote:
> > We should not call trace_handshake_cmd_done_err() if socket lookup has failed.
>
> I think Chuck would like to have a tracepoint for all the possible
> handshake_nl_done_doit() failures, but guess that could be added later
> on net-next, possibly refactoring the arguments list (e.g. adding an
> explicit fd arg, and passing explicitly a NULL sk).
>
> > Also we should call trace_handshake_cmd_done_err() before releasing the file,
> > otherwise dereferencing sock->sk can return garbage.
> >
> > This also reverts 7afc6d0a107f ("net/handshake: Fix uninitialized local variable")
>
> I can be low on coffee, but
>
>         struct handshake_req *req = NULL;
>
> is still there after this patch ?!?

Hmmm, it seems I forgot to actually commit this part :)

I will send a v2.

Re: [PATCH net] net/handshake: fix null-ptr-deref in handshake_nl_done_doit()

[Chuck Lever III]

> On Aug 31, 2023, at 3:54 AM, Paolo Abeni <pabeni@redhat.com> wrote:
> 
> On Mon, 2023-08-28 at 09:13 +0000, Eric Dumazet wrote:
>> We should not call trace_handshake_cmd_done_err() if socket lookup has failed.
> 
> I think Chuck would like to have a tracepoint for all the possible
> handshake_nl_done_doit() failures, but guess that could be added later
> on net-next, possibly refactoring the arguments list (e.g. adding an
> explicit fd arg, and passing explicitly a NULL sk).

Agree. A separate trace point that requires fewer arguments
can be added later for this case. But I don't feel like the
omission here is a show stopper.


>> Also we should call trace_handshake_cmd_done_err() before releasing the file,
>> otherwise dereferencing sock->sk can return garbage.
>> 
>> This also reverts 7afc6d0a107f ("net/handshake: Fix uninitialized local variable")
> 
> I can be low on coffee, but
> 
> struct handshake_req *req = NULL;
> 
> is still there after this patch ?!?
> 
> Cheers,
> 
> Paolo
> 

--
Chuck Lever