linux-ext4 - [patch v2] ext4: potential NULL dereference on error

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Message-ID: <20120515084640.GB30265@elgon.mountain>
Date:	Tue, 15 May 2012 11:46:40 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	"Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>
Cc:	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [patch v2] ext4: potential NULL dereference on error

The ext4_get_group_desc() function returns NULL on error, and
ext4_free_inodes_count() function dereferences it without checking.
There is a check on the next line, but it's too late.

Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
v2: cleaned up the style

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index a044a9b..ea32d7e 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -508,10 +508,12 @@ fallback_retry:
 	for (i = 0; i < ngroups; i++) {
 		grp = (parent_group + i) % ngroups;
 		desc = ext4_get_group_desc(sb, grp, NULL);
-		grp_free = ext4_free_inodes_count(sb, desc);
-		if (desc && grp_free && grp_free >= avefreei) {
-			*group = grp;
-			return 0;
+		if (desc) {
+			grp_free = ext4_free_inodes_count(sb, desc);
+			if (grp_free && grp_free >= avefreei) {
+				*group = grp;
+				return 0;
+			}
 		}
 	}
 
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