If s_reserved_gdt_blocks is extremely large, it's possible for
ext4_init_block_bitmap(), which is called when ext4 sets up an
uninitialized block bitmap, to corrupt random kernel memory. Add the
same checks which e2fsck has --- it must never be larger than
blocksize / sizeof(__u32) --- and then add a backup check in
ext4_init_block_bitmap() in case the superblock gets modified after
the file system is mounted.
Reported-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
fs/ext4/balloc.c | 3 +++
fs/ext4/super.c | 7 +++++++
2 files changed, 10 insertions(+)
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 0b8105b..799a92b 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -208,6 +208,9 @@ static int ext4_init_block_bitmap(struct super_block *sb,
memset(bh->b_data, 0, sb->s_blocksize);
bit_max = ext4_num_base_meta_clusters(sb, block_group);
+ if ((bit_max >> 3) >= bh->b_size)
+ return -EFSCORRUPTED;
+
for (bit = 0; bit < bit_max; bit++)
ext4_set_bit(bit, bh->b_data);
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 5664ee6..13c49af7 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3416,6 +3416,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
goto failed_mount;
}
+ if (le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) > (blocksize / 4)) {
+ ext4_msg(sb, KERN_ERR,
+ "Number of reserved GDT blocks insanely large: %d",
+ le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks));
+ goto failed_mount;
+ }
+
if (sbi->s_mount_opt & EXT4_MOUNT_DAX) {
err = bdev_dax_supported(sb, blocksize);
if (err)
--
2.5.0
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