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Date: Sun, 26 Mar 2017 00:20:56 +0000
From: Colin Ian King <colin.king@...onical.com>
To: Theodore Ts'o <tytso@....edu>,
Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc: stable@...r.kernel.org
Subject: Re: [PATCH -v2] ext4: lock the xattr block before checksuming it
On 25/03/17 21:24, Theodore Ts'o wrote:
> We must lock the xattr block before calculating or verifying the
> checksum in order to avoid spurious checksum failures.
>
> https://bugzilla.kernel.org/show_bug.cgi?id=193661
>
> Reported-by: Colin Ian King <colin.king@...onical.com>
> Signed-off-by: Theodore Ts'o <tytso@....edu>
> Cc: stable@...r.kernel.org
> ---
> fs/ext4/xattr.c | 65 +++++++++++++++++++++++++++------------------------------
> 1 file changed, 31 insertions(+), 34 deletions(-)
>
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 67636acf7624..996e7900d4c8 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -131,31 +131,26 @@ static __le32 ext4_xattr_block_csum(struct inode *inode,
> }
>
> static int ext4_xattr_block_csum_verify(struct inode *inode,
> - sector_t block_nr,
> - struct ext4_xattr_header *hdr)
> + struct buffer_head *bh)
> {
> - if (ext4_has_metadata_csum(inode->i_sb) &&
> - (hdr->h_checksum != ext4_xattr_block_csum(inode, block_nr, hdr)))
> - return 0;
> - return 1;
> -}
> -
> -static void ext4_xattr_block_csum_set(struct inode *inode,
> - sector_t block_nr,
> - struct ext4_xattr_header *hdr)
> -{
> - if (!ext4_has_metadata_csum(inode->i_sb))
> - return;
> + struct ext4_xattr_header *hdr = BHDR(bh);
> + int ret = 1;
>
> - hdr->h_checksum = ext4_xattr_block_csum(inode, block_nr, hdr);
> + if (ext4_has_metadata_csum(inode->i_sb)) {
> + lock_buffer(bh);
> + ret = (hdr->h_checksum == ext4_xattr_block_csum(inode,
> + bh->b_blocknr, hdr));
> + unlock_buffer(bh);
> + }
> + return ret;
> }
>
> -static inline int ext4_handle_dirty_xattr_block(handle_t *handle,
> - struct inode *inode,
> - struct buffer_head *bh)
> +static void ext4_xattr_block_csum_set(struct inode *inode,
> + struct buffer_head *bh)
> {
> - ext4_xattr_block_csum_set(inode, bh->b_blocknr, BHDR(bh));
> - return ext4_handle_dirty_metadata(handle, inode, bh);
> + if (ext4_has_metadata_csum(inode->i_sb))
> + BHDR(bh)->h_checksum = ext4_xattr_block_csum(inode,
> + bh->b_blocknr, BHDR(bh));
> }
>
> static inline const struct xattr_handler *
> @@ -233,7 +228,7 @@ ext4_xattr_check_block(struct inode *inode, struct buffer_head *bh)
> if (BHDR(bh)->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC) ||
> BHDR(bh)->h_blocks != cpu_to_le32(1))
> return -EFSCORRUPTED;
> - if (!ext4_xattr_block_csum_verify(inode, bh->b_blocknr, BHDR(bh)))
> + if (!ext4_xattr_block_csum_verify(inode, bh))
> return -EFSBADCRC;
> error = ext4_xattr_check_names(BFIRST(bh), bh->b_data + bh->b_size,
> bh->b_data);
> @@ -618,23 +613,22 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
> }
> }
>
> + ext4_xattr_block_csum_set(inode, bh);
> /*
> * Beware of this ugliness: Releasing of xattr block references
> * from different inodes can race and so we have to protect
> * from a race where someone else frees the block (and releases
> * its journal_head) before we are done dirtying the buffer. In
> * nojournal mode this race is harmless and we actually cannot
> - * call ext4_handle_dirty_xattr_block() with locked buffer as
> + * call ext4_handle_dirty_metadata() with locked buffer as
> * that function can call sync_dirty_buffer() so for that case
> * we handle the dirtying after unlocking the buffer.
> */
> if (ext4_handle_valid(handle))
> - error = ext4_handle_dirty_xattr_block(handle, inode,
> - bh);
> + error = ext4_handle_dirty_metadata(handle, inode, bh);
> unlock_buffer(bh);
> if (!ext4_handle_valid(handle))
> - error = ext4_handle_dirty_xattr_block(handle, inode,
> - bh);
> + error = ext4_handle_dirty_metadata(handle, inode, bh);
> if (IS_SYNC(inode))
> ext4_handle_sync(handle);
> dquot_free_block(inode, EXT4_C2B(EXT4_SB(inode->i_sb), 1));
> @@ -863,13 +857,14 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
> ext4_xattr_cache_insert(ext4_mb_cache,
> bs->bh);
> }
> + ext4_xattr_block_csum_set(inode, bs->bh);
> unlock_buffer(bs->bh);
> if (error == -EFSCORRUPTED)
> goto bad_block;
> if (!error)
> - error = ext4_handle_dirty_xattr_block(handle,
> - inode,
> - bs->bh);
> + error = ext4_handle_dirty_metadata(handle,
> + inode,
> + bs->bh);
> if (error)
> goto cleanup;
> goto inserted;
> @@ -967,10 +962,11 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
> ce->e_reusable = 0;
> ea_bdebug(new_bh, "reusing; refcount now=%d",
> ref);
> + ext4_xattr_block_csum_set(inode, new_bh);
> unlock_buffer(new_bh);
> - error = ext4_handle_dirty_xattr_block(handle,
> - inode,
> - new_bh);
> + error = ext4_handle_dirty_metadata(handle,
> + inode,
> + new_bh);
> if (error)
> goto cleanup_dquot;
> }
> @@ -1020,11 +1016,12 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
> goto getblk_failed;
> }
> memcpy(new_bh->b_data, s->base, new_bh->b_size);
> + ext4_xattr_block_csum_set(inode, new_bh);
> set_buffer_uptodate(new_bh);
> unlock_buffer(new_bh);
> ext4_xattr_cache_insert(ext4_mb_cache, new_bh);
> - error = ext4_handle_dirty_xattr_block(handle,
> - inode, new_bh);
> + error = ext4_handle_dirty_metadata(handle, inode,
> + new_bh);
> if (error)
> goto cleanup;
> }
>
I've given this a good soak test on 32 bit and 64 bit x86 builds and it
fixes the issue. Thanks Ted.
Tested-by: Colin Ian King <colin.king@...onical.com>
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