ext4: only look at the bg_flags field if it is valid

commit 8844618d8aa7a9973e7b527d038a2a589665002c upstream.

The bg_flags field in the block group descripts is only valid if the
uninit_bg or metadata_csum feature is enabled.  We were not
consistently looking at this field; fix this.

Also block group #0 must never have uninitialized allocation bitmaps,
or need to be zeroed, since that's where the root inode, and other
special inodes are set up.  Check for these conditions and mark the
file system as corrupted if they are detected.

This addresses CVE-2018-10876.

https://bugzilla.kernel.org/show_bug.cgi?id=199403

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

4 files changed, 36 insertions, 6 deletions

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index e632ba1e7612..f8b5635f0396 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -451,7 +451,16 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 		goto verify;
 	}
 	ext4_lock_group(sb, block_group);
-	if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
+	if (ext4_has_group_desc_csum(sb) &&
+	    (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))) {
+		if (block_group == 0) {
+			ext4_unlock_group(sb, block_group);
+			unlock_buffer(bh);
+			ext4_error(sb, "Block bitmap for bg 0 marked "
+				   "uninitialized");
+			err = -EFSCORRUPTED;
+			goto out;
+		}
 		err = ext4_init_block_bitmap(sb, bh, block_group, desc);
 		set_bitmap_uptodate(bh);
 		set_buffer_uptodate(bh);
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index df92e3ec9913..478b8f21c814 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -155,7 +155,16 @@ ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)
 	}
 
 	ext4_lock_group(sb, block_group);
-	if (desc->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)) {
+	if (ext4_has_group_desc_csum(sb) &&
+	    (desc->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT))) {
+		if (block_group == 0) {
+			ext4_unlock_group(sb, block_group);
+			unlock_buffer(bh);
+			ext4_error(sb, "Inode bitmap for bg 0 marked "
+				   "uninitialized");
+			err = -EFSCORRUPTED;
+			goto out;
+		}
 		memset(bh->b_data, 0, (EXT4_INODES_PER_GROUP(sb) + 7) / 8);
 		ext4_mark_bitmap_end(EXT4_INODES_PER_GROUP(sb),
 				     sb->s_blocksize * 8, bh->b_data);
@@ -1000,7 +1009,8 @@ got:
 
 		/* recheck and clear flag under lock if we still need to */
 		ext4_lock_group(sb, group);
-		if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
+		if (ext4_has_group_desc_csum(sb) &&
+		    (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))) {
 			gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
 			ext4_free_group_clusters_set(sb, gdp,
 				ext4_free_clusters_after_init(sb, group, gdp));
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 769a62708b1c..39187e7b3748 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2444,7 +2444,8 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
 	 * initialize bb_free to be able to skip
 	 * empty groups without initialization
 	 */
-	if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
+	if (ext4_has_group_desc_csum(sb) &&
+	    (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))) {
 		meta_group_info[i]->bb_free =
 			ext4_free_clusters_after_init(sb, group, desc);
 	} else {
@@ -3011,7 +3012,8 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
 #endif
 	ext4_set_bits(bitmap_bh->b_data, ac->ac_b_ex.fe_start,
 		      ac->ac_b_ex.fe_len);
-	if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
+	if (ext4_has_group_desc_csum(sb) &&
+	    (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))) {
 		gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
 		ext4_free_group_clusters_set(sb, gdp,
 					     ext4_free_clusters_after_init(sb,
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 29b407714aa9..140794b1ebb1 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3098,13 +3098,22 @@ static ext4_group_t ext4_has_uninit_itable(struct super_block *sb)
 	ext4_group_t group, ngroups = EXT4_SB(sb)->s_groups_count;
 	struct ext4_group_desc *gdp = NULL;
 
+	if (!ext4_has_group_desc_csum(sb))
+		return ngroups;
+
 	for (group = 0; group < ngroups; group++) {
 		gdp = ext4_get_group_desc(sb, group, NULL);
 		if (!gdp)
 			continue;
 
-		if (!(gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_ZEROED)))
+		if (gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_ZEROED))
+			continue;
+		if (group != 0)
 			break;
+		ext4_error(sb, "Inode table for bg 0 marked as "
+			   "needing zeroing");
+		if (sb_rdonly(sb))
+			return ngroups;
 	}
 
 	return group;