2017-06-10 08:47:15

by Jia-Ju Bai

Subject: [PATCH] net: caif: Fix a sleep-in-atomic bug in cfpkt_create_pfx

The kernel may sleep under a rcu read lock in cfpkt_create_pfx, and the
function call path is:
cfcnfg_linkup_rsp (acquire the lock by rcu_read_lock)
cfctrl_linkdown_req
cfpkt_create
cfpkt_create_pfx
alloc_skb(GFP_KERNEL) --> may sleep
cfserl_receive (acquire the lock by rcu_read_lock)
cfpkt_split
cfpkt_create_pfx
alloc_skb(GFP_KERNEL) --> may sleep

There is "in_interrupt" in cfpkt_create_pfx to decide use "GFP_KERNEL" or
"GFP_ATOMIC". In this situation, "GFP_KERNEL" is used because the function
is called under a rcu read lock, instead in interrupt.

To fix it, only "GFP_ATOMIC" is used in cfpkt_create_pfx.

Signed-off-by: Jia-Ju Bai <[email protected]>
---
net/caif/cfpkt_skbuff.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/net/caif/cfpkt_skbuff.c b/net/caif/cfpkt_skbuff.c
index 59ce1fc..71b6ab2 100644
--- a/net/caif/cfpkt_skbuff.c
+++ b/net/caif/cfpkt_skbuff.c
@@ -81,11 +81,7 @@ static struct cfpkt *cfpkt_create_pfx(u16 len, u16 pfx)
{
struct sk_buff *skb;

- if (likely(in_interrupt()))
- skb = alloc_skb(len + pfx, GFP_ATOMIC);
- else
- skb = alloc_skb(len + pfx, GFP_KERNEL);
-
+ skb = alloc_skb(len + pfx, GFP_ATOMIC);
if (unlikely(skb == NULL))
return NULL;

--
1.7.9.5

2017-06-10 22:21:34

by David Miller

Subject: Re: [PATCH] net: caif: Fix a sleep-in-atomic bug in cfpkt_create_pfx

From: Jia-Ju Bai <[email protected]>
Date: Sat, 10 Jun 2017 16:49:39 +0800

> The kernel may sleep under a rcu read lock in cfpkt_create_pfx, and the
> function call path is:
> cfcnfg_linkup_rsp (acquire the lock by rcu_read_lock)
> cfctrl_linkdown_req
> cfpkt_create
> cfpkt_create_pfx
> alloc_skb(GFP_KERNEL) --> may sleep
> cfserl_receive (acquire the lock by rcu_read_lock)
> cfpkt_split
> cfpkt_create_pfx
> alloc_skb(GFP_KERNEL) --> may sleep
>
> There is "in_interrupt" in cfpkt_create_pfx to decide use "GFP_KERNEL" or
> "GFP_ATOMIC". In this situation, "GFP_KERNEL" is used because the function
> is called under a rcu read lock, instead in interrupt.
>
> To fix it, only "GFP_ATOMIC" is used in cfpkt_create_pfx.
>
> Signed-off-by: Jia-Ju Bai <[email protected]>

Applied and queued up for -stable.