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[Linux-kernel-mentees,v3,net] rose: Fix Null pointer dereference in rose_send_frame()

Message ID 20201107191835.5541-1-anmol.karan123@gmail.com (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series [Linux-kernel-mentees,v3,net] rose: Fix Null pointer dereference in rose_send_frame() | expand

Commit Message

Anmol Karn Nov. 7, 2020, 7:18 p.m. UTC
rose_send_frame() dereferences `neigh->dev` when called from
rose_transmit_clear_request(), and the first occurrence of the
`neigh` is in rose_loopback_timer() as `rose_loopback_neigh`,
and it is initialized in rose_add_loopback_neigh() as NULL.
i.e when `rose_loopback_neigh` used in rose_loopback_timer()
its `->dev` was still NULL and rose_loopback_timer() was calling
rose_rx_call_request() without checking for NULL.

- net/rose/rose_link.c
This bug seems to get triggered in this line:

rose_call = (ax25_address *)neigh->dev->dev_addr;

Fix it by adding NULL checking for `rose_loopback_neigh->dev`
in rose_loopback_timer().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+a1c743815982d9496393@syzkaller.appspotmail.com
Tested-by: syzbot+a1c743815982d9496393@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=9d2a7ca8c7f2e4b682c97578dfa3f236258300b3
Signed-off-by: Anmol Karn <anmol.karan123@gmail.com>
---
Changes in v3:
        - Corrected checkpatch warnings and errors (Suggested-by: Saeed Mahameed <saeed@kernel.org>)
	- Added "Fixes:" tag (Suggested-by: Saeed Mahameed <saeed@kernel.org>)
Changes in v2:
	- Added NULL check in rose_loopback_timer() (Suggested-by: Greg KH <gregkh@linuxfoundation.org>)

 net/rose/rose_loopback.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-
2.29.2

Comments

Jakub Kicinski Nov. 10, 2020, 5:58 p.m. UTC | #1
On Sun,  8 Nov 2020 00:48:35 +0530 Anmol Karn wrote:
> +			dev = rose_dev_get(dest);

this calls dev_hold internally, you never release that reference in
case ..neigh->dev is NULL

> +			if (rose_loopback_neigh->dev && dev) {
Anmol Karn Nov. 10, 2020, 7:45 p.m. UTC | #2
Hello Sir,

On Tue, Nov 10, 2020 at 09:58:15AM -0800, Jakub Kicinski wrote:
> On Sun,  8 Nov 2020 00:48:35 +0530 Anmol Karn wrote:
> > +			dev = rose_dev_get(dest);
> 
> this calls dev_hold internally, you never release that reference in
> case ..neigh->dev is NULL
> 
> > +			if (rose_loopback_neigh->dev && dev) {

Ah, I missed to `dev_put()` the `dev` after checking for, if neigh->dev is NULL,
I will fix it soon and send another version.

Thank you for review.


Anmol
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Patch

diff --git a/net/rose/rose_loopback.c b/net/rose/rose_loopback.c
index 7b094275ea8b..2c51756ed7bf 100644
--- a/net/rose/rose_loopback.c
+++ b/net/rose/rose_loopback.c
@@ -96,7 +96,8 @@  static void rose_loopback_timer(struct timer_list *unused)
 		}

 		if (frametype == ROSE_CALL_REQUEST) {
-			if ((dev = rose_dev_get(dest)) != NULL) {
+			dev = rose_dev_get(dest);
+			if (rose_loopback_neigh->dev && dev) {
 				if (rose_rx_call_request(skb, dev, rose_loopback_neigh, lci_o) == 0)
 					kfree_skb(skb);
 			} else {