[PATCH 4.9 23/29] nfc: fix NULL ptr dereference in llcp_sock_getname() after failed connect

Greg Kroah-Hartman
2021-06-08T18:31:14Z

From: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>

commit 4ac06a1e013cf5fdd963317ffd3b968560f33bba upstream.

It's possible to trigger NULL pointer dereference by local unprivileged
user, when calling getsockname() after failed bind() (e.g. the bind
fails because LLCP_SAP_MAX used as SAP):

BUG: kernel NULL pointer dereference, address: 0000000000000000
CPU: 1 PID: 426 Comm: llcp_sock_getna Not tainted 5.13.0-rc2-next-20210521+ #9
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1 04/01/2014
Call Trace:
llcp_sock_getname+0xb1/0xe0
__sys_getpeername+0x95/0xc0
? lockdep_hardirqs_on_prepare+0xd5/0x180
? syscall_enter_from_user_mode+0x1c/0x40
__x64_sys_getpeername+0x11/0x20
do_syscall_64+0x36/0x70
entry_SYSCALL_64_after_hwframe+0x44/0xae

This can be reproduced with Syzkaller C repro (bind followed by
getpeername):
https://syzkaller.appspot.com/x/repro.c?x=14def446e00000

Cc: <stable@vger.kernel.org>
Fixes: d646960f7986 ("NFC: Initial LLCP support")
Reported-by: syzbot+80fb126e7f7d8b1a5914@syzkaller.appspotmail.com
Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210531072138.5219-1-krzysztof.kozlowski@canonical.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/nfc/llcp_sock.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/nfc/llcp_sock.c
+++ b/net/nfc/llcp_sock.c
@@ -121,6 +121,7 @@ static int llcp_sock_bind(struct socket
if (!llcp_sock->service_name) {
nfc_llcp_local_put(llcp_sock->local);
llcp_sock->local = NULL;
+ llcp_sock->dev = NULL;
ret = -ENOMEM;
goto put_dev;
}
@@ -130,6 +131,7 @@ static int llcp_sock_bind(struct socket
llcp_sock->local = NULL;
kfree(llcp_sock->service_name);
llcp_sock->service_name = NULL;
+ llcp_sock->dev = NULL;
ret = -EADDRINUSE;
goto put_dev;
}