2022-07-26 03:29:40

by Duoming Zhou

Subject: [PATCH net v2] netrom: fix sleep in atomic context bugs in timer handlers

There are sleep in atomic context bugs in timer handlers of netrom
such as nr_t1timer_expiry(), nr_t2timer_expiry(), nr_heartbeat_expiry(),
nr_idletimer_expiry() and so on.

The root cause is kmemdup() with GFP_KERNEL parameter that may sleep
could be called by different timer handlers which is in interrupt context.

One of the call paths that could trigger bug is shown below:

(interrupt context)
nr_heartbeat_expiry
nr_write_internal
nr_transmit_buffer
nr_route_frame
nr_add_node
kmemdup(..,GFP_KERNEL) //may sleep

This patch changes gfp_t parameter of kmemdup in nr_add_node()
from GFP_KERNEL to GFP_ATOMIC in order to prevent sleep in atomic
context bugs.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Duoming Zhou <[email protected]>
---
Changes in v2:
- Correct the "Fixes" tag.

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

diff --git a/net/netrom/nr_route.c b/net/netrom/nr_route.c
index baea3cbd76c..1ddcf13de6a 100644
--- a/net/netrom/nr_route.c
+++ b/net/netrom/nr_route.c
@@ -163,7 +163,7 @@ static int __must_check nr_add_node(ax25_address *nr, const char *mnemonic,
if (ax25_digi != NULL && ax25_digi->ndigi > 0) {
nr_neigh->digipeat = kmemdup(ax25_digi,
sizeof(*ax25_digi),
- GFP_KERNEL);
+ GFP_ATOMIC);
if (nr_neigh->digipeat == NULL) {
kfree(nr_neigh);
if (nr_node)
--
2.17.1

2022-07-28 02:08:15

by Jakub Kicinski

Subject: Re: [PATCH net v2] netrom: fix sleep in atomic context bugs in timer handlers

On Tue, 26 Jul 2022 11:24:20 +0800 Duoming Zhou wrote:
> nr_heartbeat_expiry
> nr_write_internal
> nr_transmit_buffer

void nr_transmit_buffer(struct sock *sk, struct sk_buff *skb)
{
[...]
if (!nr_route_frame(skb, NULL)) {

> nr_route_frame

int nr_route_frame(struct sk_buff *skb, ax25_cb *ax25)
{
[...]
if (ax25 != NULL) {
ret = nr_add_node(nr_src, "", &ax25->dest_addr, ax25->digipeat,

ax25 must be NULL on this path AFAICT.

> nr_add_node
> kmemdup(..,GFP_KERNEL) //may sleep

2022-07-28 02:28:12

by Duoming Zhou

Subject: Re: [PATCH net v2] netrom: fix sleep in atomic context bugs in timer handlers

Hello,

On Wed, 27 Jul 2022 18:36:47 -0700 Jakub Kicinski wrote:

> On Tue, 26 Jul 2022 11:24:20 +0800 Duoming Zhou wrote:
> > nr_heartbeat_expiry
> > nr_write_internal
> > nr_transmit_buffer
>
> void nr_transmit_buffer(struct sock *sk, struct sk_buff *skb)
> {
> [...]
> if (!nr_route_frame(skb, NULL)) {
>
> > nr_route_frame
>
> int nr_route_frame(struct sk_buff *skb, ax25_cb *ax25)
> {
> [...]
> if (ax25 != NULL) {
> ret = nr_add_node(nr_src, "", &ax25->dest_addr, ax25->digipeat,
>
> ax25 must be NULL on this path AFAICT.
>
> > nr_add_node
> > kmemdup(..,GFP_KERNEL) //may sleep

Thank you for your time and suggestions, I understand.

Best regards,
Duoming Zhou