linux-kernel - [PATCH] net: tipc: Fix a sleep-in-atomic bug in tipc_msg

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Date:   Sat, 10 Jun 2017 17:03:35 +0800
From:   Jia-Ju Bai <baijiaju1990@....com>
To:     jon.maloy@...csson.com, ying.xue@...driver.com, davem@...emloft.net
Cc:     netdev@...r.kernel.org, tipc-discussion@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Jia-Ju Bai <baijiaju1990@....com>
Subject: [PATCH] net: tipc: Fix a sleep-in-atomic bug in tipc_msg_reverse

The kernel may sleep under a rcu read lock in tipc_msg_reverse, and the
function call path is:
tipc_l2_rcv_msg (acquire the lock by rcu_read_lock)
  tipc_rcv
    tipc_sk_rcv
      tipc_msg_reverse
        pskb_expand_head(GFP_KERNEL) --> may sleep
tipc_node_broadcast
  tipc_node_xmit_skb
    tipc_node_xmit
      tipc_sk_rcv
        tipc_msg_reverse
          pskb_expand_head(GFP_KERNEL) --> may sleep

To fix it, "GFP_KERNEL" is replaced with "GFP_ATOMIC".

Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>
---
 net/tipc/msg.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index 312ef7d..ab30876 100644
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -508,7 +508,7 @@ bool tipc_msg_reverse(u32 own_node,  struct sk_buff **skb, int err)
 	}
 
 	if (skb_cloned(_skb) &&
-	    pskb_expand_head(_skb, BUF_HEADROOM, BUF_TAILROOM, GFP_KERNEL))
+	    pskb_expand_head(_skb, BUF_HEADROOM, BUF_TAILROOM, GFP_ATOMIC))
 		goto exit;
 
 	/* Now reverse the concerned fields */
-- 
1.7.9.5