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/balloc.c b/fs/ext4/balloc.c
index badb4e0..ad13f07 100644 (file)
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -450,7 +450,16 @@ 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 dcf63da..460866b 100644 (file)
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -152,7 +152,16 @@ 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);
@@ -926,7 +935,8 @@ 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 14bd370..53e1890 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 {
@@ -2969,7 +2970,8 @@ 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 6525127..4c5d9df 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3023,13 +3023,22 @@ 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->s_flags & MS_RDONLY)
+                       return ngroups;
        }
 
        return group;