linux-kernel - [RFC 1/1] fs/befs/linuxvfs.c: check superblock before dump operation

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Date:	Fri,  1 Aug 2014 14:50:24 +0200
From:	Fabian Frederick <fabf@...net.be>
To:	linux-kernel@...r.kernel.org
Cc:	Fabian Frederick <fabf@...net.be>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joe Perches <joe@...ches.com>
Subject: [RFC 1/1] fs/befs/linuxvfs.c: check superblock before dump operation

befs_dump_super_block was called between befs_load_sb and befs_check_sb.
It has been reported to crash (5/900) with null block testing.

This patch loads, checks and only dump superblock if it's a valid one then
brelse bh.

(befs_dump_super_block uses disk_sb (bh->b_data) so it seems we need to call
it before brelse(bh) but I don't know why befs_check_sb was called
after brelse. Another thing I don't understand is why this problem appears now).

Reported-By: Fengguang Wu <fengguang.wu@...el.com>
Cc: Fengguang Wu <fengguang.wu@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Joe Perches <joe@...ches.com>
Signed-off-by: Fabian Frederick <fabf@...net.be>
---
 fs/befs/linuxvfs.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/befs/linuxvfs.c b/fs/befs/linuxvfs.c
index a16fbd4..633d5ff 100644
--- a/fs/befs/linuxvfs.c
+++ b/fs/befs/linuxvfs.c
@@ -834,16 +834,14 @@ befs_fill_super(struct super_block *sb, void *data, int silent)
 		    (befs_super_block *) ((void *) bh->b_data + x86_sb_off);
 	}
 
-	if (befs_load_sb(sb, disk_sb) != BEFS_OK)
+	if ((befs_load_sb(sb, disk_sb) != BEFS_OK) ||
+	    (befs_check_sb(sb) != BEFS_OK))
 		goto unacquire_bh;
 
 	befs_dump_super_block(sb, disk_sb);
 
 	brelse(bh);
 
-	if (befs_check_sb(sb) != BEFS_OK)
-		goto unacquire_priv_sbp;
-
 	if( befs_sb->num_blocks > ~((sector_t)0) ) {
 		befs_error(sb, "blocks count: %llu "
 			"is larger than the host can use",
-- 
1.8.4.5

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