ext2: fix filesystem deadlock while reading corrupted xattr block

This bug can be reproducible with fsfuzzer, although, I couldn't reproduce it
100% of my tries, it is quite easily reproducible.

During the deletion of an inode, ext2_xattr_delete_inode() does not check if the
block pointed by EXT2_I(inode)->i_file_acl is a valid data block, this might
lead to a deadlock, when i_file_acl == 1, and the filesystem block size is 1024.

In that situation, ext2_xattr_delete_inode, will load the superblock's buffer
head (instead of a valid i_file_acl block), and then lock that buffer head,
which, ext2_sync_super will also try to lock, making the filesystem deadlock in
the following stack trace:

root     17180  0.0  0.0 113660   660 pts/0    D+   07:08   0:00 rmdir
/media/test/dir1

[<ffffffff8125da9f>] __sync_dirty_buffer+0xaf/0x100
[<ffffffff8125db03>] sync_dirty_buffer+0x13/0x20
[<ffffffffa03f0d57>] ext2_sync_super+0xb7/0xc0 [ext2]
[<ffffffffa03f10b9>] ext2_error+0x119/0x130 [ext2]
[<ffffffffa03e9d93>] ext2_free_blocks+0x83/0x350 [ext2]
[<ffffffffa03f3d03>] ext2_xattr_delete_inode+0x173/0x190 [ext2]
[<ffffffffa03ee9e9>] ext2_evict_inode+0xc9/0x130 [ext2]
[<ffffffff8123fd23>] evict+0xb3/0x180
[<ffffffff81240008>] iput+0x1b8/0x240
[<ffffffff8123c4ac>] d_delete+0x11c/0x150
[<ffffffff8122fa7e>] vfs_rmdir+0xfe/0x120
[<ffffffff812340ee>] do_rmdir+0x17e/0x1f0
[<ffffffff81234dd6>] SyS_rmdir+0x16/0x20
[<ffffffff81838cf2>] entry_SYSCALL_64_fastpath+0x1a/0xa4
[<ffffffffffffffff>] 0xffffffffffffffff

Fix this by using the same approach ext4 uses to test data blocks validity,
implementing ext2_data_block_valid.

An another possibility when the superblock is very corrupted, is that i_file_acl
is 1, block_count is 1 and first_data_block is 0. For such situations, we might
have i_file_acl pointing to a 'valid' block, but still step over the superblock.
The approach I used was to also test if the superblock is not in the range
described by ext2_data_block_valid() arguments

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
index 1a5e3bff0b63..b7f896f3f7a7 100644
--- a/fs/ext2/xattr.c
+++ b/fs/ext2/xattr.c
@@ -759,10 +759,19 @@ void
 ext2_xattr_delete_inode(struct inode *inode)
 {
 	struct buffer_head *bh = NULL;
+	struct ext2_sb_info *sbi = EXT2_SB(inode->i_sb);
 
 	down_write(&EXT2_I(inode)->xattr_sem);
 	if (!EXT2_I(inode)->i_file_acl)
 		goto cleanup;
+
+	if (!ext2_data_block_valid(sbi, EXT2_I(inode)->i_file_acl, 0)) {
+		ext2_error(inode->i_sb, "ext2_xattr_delete_inode",
+			"inode %ld: xattr block %d is out of data blocks range",
+			inode->i_ino, EXT2_I(inode)->i_file_acl);
+		goto cleanup;
+	}
+
 	bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl);
 	if (!bh) {
 		ext2_error(inode->i_sb, "ext2_xattr_delete_inode",