linux-kernel - [127/127] x86: uv: xpc NULL deref when mesq becomes empty

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Date:	Tue, 07 Dec 2010 16:45:13 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Robin Holt <holt@....com>, Jack Steiner <steiner@....com>,
	Ingo Molnar <mingo@...e.hu>
Subject: [127/127] x86: uv: xpc NULL deref when mesq becomes empty

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Robin Holt <holt@....com>

commit 15b87d67ff3dc042bee42f991858d6b121b3b3ca upstream.

Under heavy load conditions, our set of xpc messages may become exhausted.
 The code handles this correctly with the exception of the management code
which hits a NULL pointer dereference.

Signed-off-by: Robin Holt <holt@....com>
Cc: Jack Steiner <steiner@....com>
Cc: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/misc/sgi-xp/xpc_uv.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/misc/sgi-xp/xpc_uv.c
+++ b/drivers/misc/sgi-xp/xpc_uv.c
@@ -965,11 +965,13 @@ xpc_get_fifo_entry_uv(struct xpc_fifo_he
 		head->first = first->next;
 		if (head->first == NULL)
 			head->last = NULL;
+
+		head->n_entries--;
+		BUG_ON(head->n_entries < 0);
+
+		first->next = NULL;
 	}
-	head->n_entries--;
-	BUG_ON(head->n_entries < 0);
 	spin_unlock_irqrestore(&head->lock, irq_flags);
-	first->next = NULL;
 	return first;
 }
 


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