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

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

[Duoming Zhou]

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 <duoming@zju.edu.cn>
---
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

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

[Jakub Kicinski]

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

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

[duoming]

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