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>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 14bd370..53e1890 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2444,7 +2444,8 @@
* 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 {
@@ -2969,7 +2970,8 @@
#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,