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

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

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 8a2e202ade8a03116601d71b30ab4ff815f4708c..e68cefe082612c84b39c612ef3ff32fca8ac3d25 100644 (file)
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -438,7 +438,16 @@ 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 4d6e007f3569a5440398e2c0f5e88fc1fea7225e..da6c10c1e37aa97d1e715586a8c57f699289ea1f 100644 (file)
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -150,7 +150,16 @@ 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);
@@ -994,7 +1003,8 @@ 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 243c42fdc155483922b60b95c69f2c79811bfd1a..402c769c51ea16d4ccb0ef6114c5f7f58a593c2b 100644 (file)
--- 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 {
@@ -3010,7 +3011,8 @@ 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 c61675d62195c2b62e712cf6e6e124f0002c175d..4d34430d75f61b05a790fb3b938c42e63d14babd 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3139,13 +3139,22 @@ 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;