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

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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
This commit is contained in:
Theodore Ts'o 2018-06-14 00:58:00 -04:00
parent 77260807d1
commit 8844618d8a
4 changed files with 36 additions and 6 deletions
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11
fs/ext4/balloc.c
View file

@ -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);