linux-ext4 - [PATCH V2] ext4: ext4_mb_seq_groups_show: Fix stack memory corruption

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Message-Id: <1478756764-4459-1-git-send-email-chandan@linux.vnet.ibm.com>
Date:   Thu, 10 Nov 2016 11:16:04 +0530
From:   Chandan Rajendra <chandan@...ux.vnet.ibm.com>
To:     linux-ext4@...r.kernel.org
Cc:     Chandan Rajendra <chandan@...ux.vnet.ibm.com>, tytso@....edu,
        jack@...e.cz, adilger@...ger.ca
Subject: [PATCH V2] ext4: ext4_mb_seq_groups_show: Fix stack memory corruption

The number of 'counters' elements needed in 'struct sg' is
super_block->s_blocksize_bits + 2. Presently we have 16 'counters'
elements in the array. This is insufficient for block sizes >= 32k. In
such cases the memcpy operation performed in ext4_mb_seq_groups_show()
would cause stack memory corruption.

Signed-off-by: Chandan Rajendra <chandan@...ux.vnet.ibm.com>
---
Changelog: 
v1->v2: Use EXT4_MAX_BLOCK_LOG_SIZE instead of the integer constant 16.

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

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index a937ac7..7ae43c5 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2287,7 +2287,7 @@ static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
 	struct ext4_group_info *grinfo;
 	struct sg {
 		struct ext4_group_info info;
-		ext4_grpblk_t counters[16];
+		ext4_grpblk_t counters[EXT4_MAX_BLOCK_LOG_SIZE + 2];
 	} sg;
 
 	group--;
-- 
2.5.5

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