Re: [PATCH] Fix filesystem deadlock while reading corrupted xattr block

[Carlos Maiolino <cmaiolino@redhat.com>]

On Tue, Jun 28, 2016 at 12:42:46PM +0200, Carlos Maiolino wrote:

I apologize, I should have mentioned in the $SUBJ it is an EXT2 patch.


> 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>
> ---
>  fs/ext2/balloc.c | 21 +++++++++++++++++++++
>  fs/ext2/ext2.h   |  3 +++
>  fs/ext2/inode.c  | 10 ++++++++++
>  fs/ext2/xattr.c  |  9 +++++++++
>  4 files changed, 43 insertions(+)
> 
> diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
> index 9f9992b..4c40c07 100644
> --- a/fs/ext2/balloc.c
> +++ b/fs/ext2/balloc.c
> @@ -1194,6 +1194,27 @@ static int ext2_has_free_blocks(struct ext2_sb_info *sbi)
>  }
>  
>  /*
> + * Returns 1 if the passed-in block region is valid; 0 if some part overlaps
> + * with filesystem metadata blocksi.
> + */
> +int ext2_data_block_valid(struct ext2_sb_info *sbi, ext2_fsblk_t start_blk,
> +			  unsigned int count)
> +{
> +	if ((start_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
> +	    (start_blk + count < start_blk) ||
> +	    (start_blk > le32_to_cpu(sbi->s_es->s_blocks_count)))
> +		return 0;
> +
> +	/* Ensure we do not step over superblock */
> +	if ((start_blk <= sbi->s_sb_block) &&
> +	    (start_blk + count >= sbi->s_sb_block))
> +		return 0;
> +
> +
> +	return 1;
> +}
> +
> +/*
>   * ext2_new_blocks() -- core block(s) allocation function
>   * @inode:		file inode
>   * @goal:		given target block(filesystem wide)
> diff --git a/fs/ext2/ext2.h b/fs/ext2/ext2.h
> index 170939f..3fb9368 100644
> --- a/fs/ext2/ext2.h
> +++ b/fs/ext2/ext2.h
> @@ -367,6 +367,7 @@ struct ext2_inode {
>   */
>  #define	EXT2_VALID_FS			0x0001	/* Unmounted cleanly */
>  #define	EXT2_ERROR_FS			0x0002	/* Errors detected */
> +#define	EFSCORRUPTED			EUCLEAN	/* Filesystem is corrupted */
>  
>  /*
>   * Mount flags
> @@ -739,6 +740,8 @@ extern unsigned long ext2_bg_num_gdb(struct super_block *sb, int group);
>  extern ext2_fsblk_t ext2_new_block(struct inode *, unsigned long, int *);
>  extern ext2_fsblk_t ext2_new_blocks(struct inode *, unsigned long,
>  				unsigned long *, int *);
> +extern int ext2_data_block_valid(struct ext2_sb_info *sbi, ext2_fsblk_t start_blk,
> +				 unsigned int count);
>  extern void ext2_free_blocks (struct inode *, unsigned long,
>  			      unsigned long);
>  extern unsigned long ext2_count_free_blocks (struct super_block *);
> diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> index fcbe586..d5c7d09 100644
> --- a/fs/ext2/inode.c
> +++ b/fs/ext2/inode.c
> @@ -1389,6 +1389,16 @@ struct inode *ext2_iget (struct super_block *sb, unsigned long ino)
>  	ei->i_frag_size = raw_inode->i_fsize;
>  	ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl);
>  	ei->i_dir_acl = 0;
> +
> +	if (ei->i_file_acl &&
> +	    !ext2_data_block_valid(EXT2_SB(sb), ei->i_file_acl, 1)) {
> +		ext2_error(sb, "ext2_iget", "bad extended attribute block %u",
> +			   ei->i_file_acl);
> +		brelse(bh);
> +		ret = -EFSCORRUPTED;
> +		goto bad_inode;
> +	}
> +
>  	if (S_ISREG(inode->i_mode))
>  		inode->i_size |= ((__u64)le32_to_cpu(raw_inode->i_size_high)) << 32;
>  	else
> diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
> index 1a5e3bf..b7f896f 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",
> -- 
> 2.4.11
> 
> --
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-- 
Carlos