ext4: fix stack memory corruption with 64k block size

commit 30a9d7afe70ed6bd9191d3000e2ef1a34fb58493 upstream.

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.

Fixes: c9de560ded61f
Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 3338f353687f37686de7c9cfb51e536ffb4ce75b..ebc50aa7347c8f486a7fd7438f5c6de91b0e3ab4 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2134,7 +2134,7 @@ static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
        struct ext4_buddy e4b;
        struct sg {
                struct ext4_group_info info;
-               ext4_grpblk_t counters[16];
+               ext4_grpblk_t counters[EXT4_MAX_BLOCK_LOG_SIZE + 2];
        } sg;
 
        group--;