[PATCH] ext4: validate s_reserved_gdt_blocks on mount
From: Theodore Ts'o <tytso@mit.edu>
Date: 2016-07-06 00:03:24
Also in:
stable
Subsystem:
ext4 file system, filesystems (vfs and infrastructure), the rest · Maintainers:
"Theodore Ts'o", Alexander Viro, Christian Brauner, Linus Torvalds
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 <redacted> Signed-off-by: Theodore Ts'o <tytso@mit.edu> Cc: stable@vger.kernel.org --- 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