linux-ext4 - [RFC 12/20] ext4: mballoc: Fix possible NULL ptr dereference from mb_cmp

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Date:   Fri,  1 May 2020 11:59:54 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        linux-fsdevel@...r.kernel.org, Jan Kara <jack@...e.com>,
        tytso@....edu, "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: [RFC 12/20] ext4: mballoc: Fix possible NULL ptr dereference from mb_cmp_bitmaps()

Make sure to check for e4b->bd_info->bb_bitmap == NULL, in
mb_cmp_bitmaps() and return if NULL, to avoid possible NULL ptr
dereference. Similar to how we do this in other ifdef DOUBLE_CHECK
functions.

Signed-off-by: Ritesh Harjani <riteshh@...ux.ibm.com>
---
 fs/ext4/mballoc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 5e59c18c89c0..e32f3675f962 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -522,6 +522,8 @@ static void mb_mark_used_double(struct ext4_buddy *e4b, int first, int count)
 
 static void mb_cmp_bitmaps(struct ext4_buddy *e4b, void *bitmap)
 {
+	if (unlikely(e4b->bd_info->bb_bitmap == NULL))
+		return;
 	if (memcmp(e4b->bd_info->bb_bitmap, bitmap, e4b->bd_sb->s_blocksize)) {
 		unsigned char *b1, *b2;
 		int i;
-- 
2.21.0