linux-kernel - [27/45] ext4: Avoid null pointer dereference when decoding EROFS w/o a journal

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Message-Id: <20100330224958.030460178@linux.site>
Date:	Tue, 30 Mar 2010 15:48:47 -0700
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,
	Eric Sesterhenn <eric.sesterhenn@...xperts.de>,
	"Theodore Tso" <tytso@....edu>, Greg Kroah-Hartman <gregkh@...e.de>
Subject: [27/45] ext4: Avoid null pointer dereference when decoding EROFS w/o a journal

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

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

From: Theodore Ts'o <tytso@....edu>

commit 78f1ddbb498283c2445c11b0dfa666424c301803 upstream.

We need to check to make sure a journal is present before checking the
journal flags in ext4_decode_error().

Signed-off-by: Eric Sesterhenn <eric.sesterhenn@...xperts.de>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/ext4/super.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -254,7 +254,8 @@ static const char *ext4_decode_error(str
 		errstr = "Out of memory";
 		break;
 	case -EROFS:
-		if (!sb || EXT4_SB(sb)->s_journal->j_flags & JBD2_ABORT)
+		if (!sb || (EXT4_SB(sb)->s_journal &&
+			    EXT4_SB(sb)->s_journal->j_flags & JBD2_ABORT))
 			errstr = "Journal has aborted";
 		else
 			errstr = "Readonly filesystem";


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