Patch "ext4: validate s_reserved_gdt_blocks on mount" has been added to the 4.6-stable tree

This is a note to let you know that I've just added the patch titled

ext4: validate s_reserved_gdt_blocks on mount

to the 4.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-validate-s_reserved_gdt_blocks-on-mount.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Theodore Ts'o <[email protected]>
Date: Tue, 5 Jul 2016 20:01:52 -0400
Subject: ext4: validate s_reserved_gdt_blocks on mount

From: Theodore Ts'o <[email protected]>

commit 5b9554dc5bf008ae7f68a52e3d7e76c0920938a2 upstream.

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.

---
 fs/ext4/balloc.c |    3 +++
 fs/ext4/super.c  |    7 +++++++
 2 files changed, 10 insertions(+)

@@ -208,6 +208,9 @@ static int ext4_init_block_bitmap(struct
 	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);
 

@@ -3415,6 +3415,13 @@ static int ext4_fill_super(struct super_
 		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) {
 		if (blocksize != PAGE_SIZE) {
 			ext4_msg(sb, KERN_ERR,

Patches currently in stable-queue which might be from [email protected] are

queue-4.6/ext4-fix-deadlock-during-page-writeback.patch queue-4.6/ext4-short-cut-orphan-cleanup-on-error.patch queue-4.6/ext4-check-for-extents-that-wrap-around.patch queue-4.6/ext4-validate-s_reserved_gdt_blocks-on-mount.patch queue-4.6/ext4-don-t-call-ext4_should_journal_data-on-the-journal-inode.patch queue-4.6/random-strengthen-input-validation-for-rndaddtoentcnt.patch