linux-kernel - [ 068/120] ext4: fix crash when accessing /proc/mounts concurrently

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Date:	Thu, 11 Oct 2012 10:00:20 +0900
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk,
	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>,
	"Theodore Tso" <tytso@....edu>, Brad Figg <brad.figg@...onical.com>
Subject: [ 068/120] ext4: fix crash when accessing /proc/mounts concurrently

3.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>

commit 50df9fd55e4271e89a7adf3b1172083dd0ca199d upstream.

The crash was caused by a variable being erronously declared static in
token2str().

In addition to /proc/mounts, the problem can also be easily replicated
by accessing /proc/fs/ext4/<partition>/options in parallel:

$ cat /proc/fs/ext4/<partition>/options > options.txt

... and then running the following command in two different terminals:

$ while diff /proc/fs/ext4/<partition>/options options.txt; do true; done

This is also the cause of the following a crash while running xfstests
#234, as reported in the following bug reports:

	https://bugs.launchpad.net/bugs/1053019
	https://bugzilla.kernel.org/show_bug.cgi?id=47731

Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Cc: Brad Figg <brad.figg@...onical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/ext4/super.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1692,7 +1692,7 @@ static inline void ext4_show_quota_optio
 
 static const char *token2str(int token)
 {
-	static const struct match_token *t;
+	const struct match_token *t;
 
 	for (t = tokens; t->token != Opt_err; t++)
 		if (t->token == token && !strchr(t->pattern, '='))


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