[2/2] f2fs: fix error handling in f2fs_end_enable_verity()

From: Eric Biggers <ebiggers@google.com>

f2fs didn't properly clean up if verity failed to be enabled on a file:

- It left verity metadata (pages past EOF) in the page cache, which
  would be exposed to userspace if the file was later extended.

- It didn't truncate the verity metadata at all (either from cache or
  from disk) if an error occurred while setting the verity bit.

Fix these bugs by adding a call to truncate_inode_pages() and ensuring
that we truncate the verity metadata (both from cache and from disk) in
all error paths.  Also rework the code to cleanly separate the success
path from the error paths, which makes it much easier to understand.

Reported-by: Yunlei He <heyunlei@hihonor.com>
Fixes: 95ae251fe828 ("f2fs: add fs-verity support")
Cc: <stable@vger.kernel.org> # v5.4+
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/f2fs/verity.c | 61 ++++++++++++++++++++++++++++++++----------------
 1 file changed, 41 insertions(+), 20 deletions(-)

On 2021/3/3 4:04, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> f2fs didn't properly clean up if verity failed to be enabled on a file:
> 
> - It left verity metadata (pages past EOF) in the page cache, which
>    would be exposed to userspace if the file was later extended.
> 
> - It didn't truncate the verity metadata at all (either from cache or
>    from disk) if an error occurred while setting the verity bit.
> 
> Fix these bugs by adding a call to truncate_inode_pages() and ensuring
> that we truncate the verity metadata (both from cache and from disk) in
> all error paths.  Also rework the code to cleanly separate the success
> path from the error paths, which makes it much easier to understand.
> 
> Reported-by: Yunlei He <heyunlei@hihonor.com>
> Fixes: 95ae251fe828 ("f2fs: add fs-verity support")
> Cc: <stable@vger.kernel.org> # v5.4+
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>   fs/f2fs/verity.c | 61 ++++++++++++++++++++++++++++++++----------------
>   1 file changed, 41 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/f2fs/verity.c b/fs/f2fs/verity.c
> index 054ec852b5ea4..2db89967fde37 100644
> --- a/fs/f2fs/verity.c
> +++ b/fs/f2fs/verity.c
> @@ -160,31 +160,52 @@ static int f2fs_end_enable_verity(struct file *filp, const void *desc,
>   	};
>   	int err = 0;
>   
> -	if (desc != NULL) {
> -		/* Succeeded; write the verity descriptor. */
> -		err = pagecache_write(inode, desc, desc_size, desc_pos);
> +	/*
> +	 * If an error already occurred (which fs/verity/ signals by passing
> +	 * desc == NULL), then only clean-up is needed.
> +	 */
> +	if (desc == NULL)
> +		goto cleanup;
>   
> -		/* Write all pages before clearing FI_VERITY_IN_PROGRESS. */
> -		if (!err)
> -			err = filemap_write_and_wait(inode->i_mapping);
> -	}
> +	/* Append the verity descriptor. */
> +	err = pagecache_write(inode, desc, desc_size, desc_pos);
> +	if (err)
> +		goto cleanup;
>   
> -	/* If we failed, truncate anything we wrote past i_size. */
> -	if (desc == NULL || err)
> -		f2fs_truncate(inode);
> +	/*
> +	 * Write all pages (both data and verity metadata).  Note that this must
> +	 * happen before clearing FI_VERITY_IN_PROGRESS; otherwise pages beyond
> +	 * i_size won't be written properly.  For crash consistency, this also
> +	 * must happen before the verity inode flag gets persisted.
> +	 */
> +	err = filemap_write_and_wait(inode->i_mapping);
> +	if (err)
> +		goto cleanup;
> +
> +	/* Set the verity xattr. */
> +	err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
> +			    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
> +			    NULL, XATTR_CREATE);
> +	if (err)
> +		goto cleanup;
> +
> +	/* Finally, set the verity inode flag. */
> +	file_set_verity(inode);
> +	f2fs_set_inode_flags(inode);
> +	f2fs_mark_inode_dirty_sync(inode, true);
>   
>   	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
> +	return 0;
>   
> -	if (desc != NULL && !err) {
> -		err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
> -				    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
> -				    NULL, XATTR_CREATE);
> -		if (!err) {
> -			file_set_verity(inode);
> -			f2fs_set_inode_flags(inode);
> -			f2fs_mark_inode_dirty_sync(inode, true);
> -		}
> -	}
> +cleanup:
> +	/*
> +	 * Verity failed to be enabled, so clean up by truncating any verity
> +	 * metadata that was written beyond i_size (both from cache and from
> +	 * disk) and clearing FI_VERITY_IN_PROGRESS.
> +	 */
> +	truncate_inode_pages(inode->i_mapping, inode->i_size);
> +	f2fs_truncate(inode);

Eric,

Truncation can fail due to a lot of reasons, if we fail in f2fs_truncate(),
do we need to at least print a message here? or it allows to keep those
meta/data silently.

One other concern is that how do you think of covering truncate_inode_pages &
f2fs_truncate with F2FS_I(inode)->i_gc_rwsem[WRITE] lock to avoid racing with
GC, so that page cache won't be revalidated after truncate_inode_pages().

Thanks,

> +	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS); >   	return err;
>   }
>   
>

On Fri, Mar 05, 2021 at 09:37:26AM +0800, Chao Yu wrote:
> > +cleanup:
> > +	/*
> > +	 * Verity failed to be enabled, so clean up by truncating any verity
> > +	 * metadata that was written beyond i_size (both from cache and from
> > +	 * disk) and clearing FI_VERITY_IN_PROGRESS.
> > +	 */
> > +	truncate_inode_pages(inode->i_mapping, inode->i_size);
> > +	f2fs_truncate(inode);
> 
> Eric,
> 
> Truncation can fail due to a lot of reasons, if we fail in f2fs_truncate(),
> do we need to at least print a message here? or it allows to keep those
> meta/data silently.

I suppose we might as well, although hopefully there will already be a message
for the underlying failure reason too.  Also, f2fs_file_write_iter() has the
same issue too, right?

> One other concern is that how do you think of covering truncate_inode_pages &
> f2fs_truncate with F2FS_I(inode)->i_gc_rwsem[WRITE] lock to avoid racing with
> GC, so that page cache won't be revalidated after truncate_inode_pages().

Yes, that does seem to be needed, due to the way the f2fs garbage collection
works.

- Eric