From 99b8874e79619498ade354357f64299768642af6 Mon Sep 17 00:00:00 2001 From: Srinivas Eeda Date: Tue, 10 Feb 2015 14:09:26 -0800 Subject: [PATCH] o2dlm: fix NULL pointer dereference in o2dlm_blocking_ast_wrapper A tiny race between BAST and unlock message causes the NULL dereference. A node sends an unlock request to master and receives a response. Before processing the response it receives a BAST from the master. Since both requests are processed by different threads it creates a race. While the BAST is being processed, lock can get freed by unlock code. This patch makes bast to return immediately if lock is found but unlock is pending. The code should handle this race. We also have to fix master node to skip sending BAST after receiving unlock message. Below is the crash stack BUG: unable to handle kernel NULL pointer dereference at 0000000000000048 IP: o2dlm_blocking_ast_wrapper+0xd/0x16 dlm_do_local_bast+0x8e/0x97 [ocfs2_dlm] dlm_proxy_ast_handler+0x838/0x87e [ocfs2_dlm] o2net_process_message+0x395/0x5b8 [ocfs2_nodemanager] o2net_rx_until_empty+0x762/0x90d [ocfs2_nodemanager] worker_thread+0x14d/0x1ed [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Srinivas Eeda Reviewed-by: Mark Fasheh Cc: Joel Becker Cc: Joseph Qi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/ocfs2/dlm/dlmast.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/ocfs2/dlm/dlmast.c b/fs/ocfs2/dlm/dlmast.c index b46278f9ae44..fd6bbbbd7d78 100644 --- a/fs/ocfs2/dlm/dlmast.c +++ b/fs/ocfs2/dlm/dlmast.c @@ -385,8 +385,12 @@ int dlm_proxy_ast_handler(struct o2net_msg *msg, u32 len, void *data, head = &res->granted; list_for_each_entry(lock, head, list) { - if (lock->ml.cookie == cookie) + /* if lock is found but unlock is pending ignore the bast */ + if (lock->ml.cookie == cookie) { + if (lock->unlock_pending) + break; goto do_ast; + } } mlog(0, "Got %sast for unknown lock! cookie=%u:%llu, name=%.*s, "