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 7d3451808bf3c52f60cb5d2c7ebedab9c098cd8b..092da164bdc0b83a91fbeb6eb49cbf8b9d6a5a02 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 9fe55b7d4c2c73d1c811789ef10f78d88d47264b..48d818eba9c3388d50c7c945cd1366de608d7e11 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);
@@ -919,7 +928,8 @@ 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 d98ff184d94aca53c9e24f92f615e2303eec166f..75f79ff29ce020a30dd4814452a66bc60a0f4cd2 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2445,7 +2445,8 @@ 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 {
@@ -2966,7 +2967,8 @@ 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 88409168cc1e18ad79fb481fec236a9112e46c4f..4cff3ff7b9e0db5a4d70779a07e59caf98096e55 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2867,13 +2867,22 @@ 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;