Re: [PATCH v15] vfs: fix copy_file_range() regression in cross-fs copies

["Luís Henriques" <lhenriques@suse.de>]

On Wed, Jun 15, 2022 at 04:00:14PM +0300, Amir Goldstein wrote:
> A regression has been reported by Nicolas Boichat, found while using the
> copy_file_range syscall to copy a tracefs file.  Before commit
> 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices") the
> kernel would return -EXDEV to userspace when trying to copy a file across
> different filesystems.  After this commit, the syscall doesn't fail anymore
> and instead returns zero (zero bytes copied), as this file's content is
> generated on-the-fly and thus reports a size of zero.
> 
> Another regression has been reported by He Zhe - the assertion of
> WARN_ON_ONCE(ret == -EOPNOTSUPP) can be triggered from userspace when
> copying from a sysfs file whose read operation may return -EOPNOTSUPP.
> 
> Since we do not have test coverage for copy_file_range() between any
> two types of filesystems, the best way to avoid these sort of issues
> in the future is for the kernel to be more picky about filesystems that
> are allowed to do copy_file_range().
> 
> This patch restores some cross-filesystem copy restrictions that existed
> prior to commit 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
> devices"), namely, cross-sb copy is not allowed for filesystems that do
> not implement ->copy_file_range().
> 
> Filesystems that do implement ->copy_file_range() have full control of
> the result - if this method returns an error, the error is returned to
> the user.  Before this change this was only true for fs that did not
> implement the ->remap_file_range() operation (i.e. nfsv3).
> 
> Filesystems that do not implement ->copy_file_range() still fall-back to
> the generic_copy_file_range() implementation when the copy is within the
> same sb.  This helps the kernel can maintain a more consistent story
> about which filesystems support copy_file_range().
> 
> nfsd and ksmbd servers are modified to fall-back to the
> generic_copy_file_range() implementation in case vfs_copy_file_range()
> fails with -EOPNOTSUPP or -EXDEV, which preserves behavior of
> server-side-copy.
> 
> fall-back to generic_copy_file_range() is not implemented for the smb
> operation FSCTL_DUPLICATE_EXTENTS_TO_FILE, which is arguably a correct
> change of behavior.
> 
> Fixes: 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices")
> Link: https://lore.kernel.org/linux-fsdevel/20210212044405.4120619-1-drinkcat@chromium.org/
> Link: https://lore.kernel.org/linux-fsdevel/CANMq1KDZuxir2LM5jOTm0xx+BnvW=ZmpsG47CyHFJwnw7zSX6Q@mail.gmail.com/
> Link: https://lore.kernel.org/linux-fsdevel/20210126135012.1.If45b7cdc3ff707bc1efa17f5366057d60603c45f@changeid/
> Link: https://lore.kernel.org/linux-fsdevel/20210630161320.29006-1-lhenriques@suse.de/
> Reported-by: Nicolas Boichat <drinkcat@chromium.org>
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Signed-off-by: Luis Henriques <lhenriques@suse.de>
> Fixes: 64bf5ff58dff ("vfs: no fallback for ->copy_file_range")
> Link: https://lore.kernel.org/linux-fsdevel/20f17f64-88cb-4e80-07c1-85cb96c83619@windriver.com/
> Reported-by: He Zhe <zhe.he@windriver.com>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
> Hi Luis, Namje,
> 
> Thank you for testing v14 [1].  Unfortunately (or fortunately),
> kernel test robot has alerted me on LTP test failure [2] with v14.
> 
> The patch had changed behavior of same sb case when it should not have.
> So I did not apply you Tested-by and I would like to request from you
> to test v15.

Thanks, Amir.  Again, I didn't found any issues while testing this patch
on ceph.  So, feel free to add my:

Tested-by: Luís Henriques <lhenriques@suse.de>

Cheers,
--
Luís

> 
> Luis,
> 
> since you gave your concent and a lot has changed since your last
> posting, I had assumed (back) authorship of this patch and kept your
> original Signed-off-by.
> 
> Steve, Olga,
> 
> if you guys could also test v15 that would be great.
> I had tested myself using fstests as described in v14 and with LTP.
> 
> Thanks,
> Amir.
> 
> Changes since v14 [1]:
> - Allow fallback to generic_copy_file_range() within same sb
> - Run the LTP copy_file_range tests
> - Assume patch authorship
> 
> Changes since v13:
> - Rebased and tested over 5.19-rc1
> - Never fallback from ->copy_file_range() to generic_copy_file_range()
> - Added fallback to generic_copy_file_range() in ksmbd
> - Typo fixes in commit message and comments
> 
> [1] https://lore.kernel.org/linux-fsdevel/20220606134608.684131-1-amir73il@gmail.com/
> [2] https://lore.kernel.org/linux-fsdevel/CAOQ4uxgHPgFTWBOF34=UDtaCOk0EA6f=66szS-Ox62YNPx1b=A@mail.gmail.com/
> 
>  fs/ksmbd/smb2pdu.c | 16 ++++++++--
>  fs/ksmbd/vfs.c     |  4 +++
>  fs/nfsd/vfs.c      |  8 ++++-
>  fs/read_write.c    | 77 ++++++++++++++++++++++++++--------------------
>  4 files changed, 68 insertions(+), 37 deletions(-)
> 
> diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
> index e6f4ccc12f49..17f42f5b02fe 100644
> --- a/fs/ksmbd/smb2pdu.c
> +++ b/fs/ksmbd/smb2pdu.c
> @@ -7806,14 +7806,24 @@ int smb2_ioctl(struct ksmbd_work *work)
>  		src_off = le64_to_cpu(dup_ext->SourceFileOffset);
>  		dst_off = le64_to_cpu(dup_ext->TargetFileOffset);
>  		length = le64_to_cpu(dup_ext->ByteCount);
> -		cloned = vfs_clone_file_range(fp_in->filp, src_off, fp_out->filp,
> -					      dst_off, length, 0);
> +		/*
> +		 * XXX: It is not clear if FSCTL_DUPLICATE_EXTENTS_TO_FILE
> +		 * should fall back to vfs_copy_file_range().  This could be
> +		 * beneficial when re-exporting nfs/smb mount, but note that
> +		 * this can result in partial copy that returns an error status.
> +		 * If/when FSCTL_DUPLICATE_EXTENTS_TO_FILE_EX is implemented,
> +		 * fall back to vfs_copy_file_range(), should be avoided when
> +		 * the flag DUPLICATE_EXTENTS_DATA_EX_SOURCE_ATOMIC is set.
> +		 */
> +		cloned = vfs_clone_file_range(fp_in->filp, src_off,
> +					      fp_out->filp, dst_off, length, 0);
>  		if (cloned == -EXDEV || cloned == -EOPNOTSUPP) {
>  			ret = -EOPNOTSUPP;
>  			goto dup_ext_out;
>  		} else if (cloned != length) {
>  			cloned = vfs_copy_file_range(fp_in->filp, src_off,
> -						     fp_out->filp, dst_off, length, 0);
> +						     fp_out->filp, dst_off,
> +						     length, 0);
>  			if (cloned != length) {
>  				if (cloned < 0)
>  					ret = cloned;
> diff --git a/fs/ksmbd/vfs.c b/fs/ksmbd/vfs.c
> index dcdd07c6efff..8d57347231ce 100644
> --- a/fs/ksmbd/vfs.c
> +++ b/fs/ksmbd/vfs.c
> @@ -1777,6 +1777,10 @@ int ksmbd_vfs_copy_file_ranges(struct ksmbd_work *work,
>  
>  		ret = vfs_copy_file_range(src_fp->filp, src_off,
>  					  dst_fp->filp, dst_off, len, 0);
> +		if (ret == -EOPNOTSUPP || ret == -EXDEV)
> +			ret = generic_copy_file_range(src_fp->filp, src_off,
> +						      dst_fp->filp, dst_off,
> +						      len, 0);
>  		if (ret < 0)
>  			return ret;
>  
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 840e3af63a6f..b764213bcc55 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -577,6 +577,7 @@ __be32 nfsd4_clone_file_range(struct svc_rqst *rqstp,
>  ssize_t nfsd_copy_file_range(struct file *src, u64 src_pos, struct file *dst,
>  			     u64 dst_pos, u64 count)
>  {
> +	ssize_t ret;
>  
>  	/*
>  	 * Limit copy to 4MB to prevent indefinitely blocking an nfsd
> @@ -587,7 +588,12 @@ ssize_t nfsd_copy_file_range(struct file *src, u64 src_pos, struct file *dst,
>  	 * limit like this and pipeline multiple COPY requests.
>  	 */
>  	count = min_t(u64, count, 1 << 22);
> -	return vfs_copy_file_range(src, src_pos, dst, dst_pos, count, 0);
> +	ret = vfs_copy_file_range(src, src_pos, dst, dst_pos, count, 0);
> +
> +	if (ret == -EOPNOTSUPP || ret == -EXDEV)
> +		ret = generic_copy_file_range(src, src_pos, dst, dst_pos,
> +					      count, 0);
> +	return ret;
>  }
>  
>  __be32 nfsd4_vfs_fallocate(struct svc_rqst *rqstp, struct svc_fh *fhp,
> diff --git a/fs/read_write.c b/fs/read_write.c
> index b1b1cdfee9d3..c77df4ca6558 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1397,28 +1397,6 @@ ssize_t generic_copy_file_range(struct file *file_in, loff_t pos_in,
>  }
>  EXPORT_SYMBOL(generic_copy_file_range);
>  
> -static ssize_t do_copy_file_range(struct file *file_in, loff_t pos_in,
> -				  struct file *file_out, loff_t pos_out,
> -				  size_t len, unsigned int flags)
> -{
> -	/*
> -	 * Although we now allow filesystems to handle cross sb copy, passing
> -	 * a file of the wrong filesystem type to filesystem driver can result
> -	 * in an attempt to dereference the wrong type of ->private_data, so
> -	 * avoid doing that until we really have a good reason.  NFS defines
> -	 * several different file_system_type structures, but they all end up
> -	 * using the same ->copy_file_range() function pointer.
> -	 */
> -	if (file_out->f_op->copy_file_range &&
> -	    file_out->f_op->copy_file_range == file_in->f_op->copy_file_range)
> -		return file_out->f_op->copy_file_range(file_in, pos_in,
> -						       file_out, pos_out,
> -						       len, flags);
> -
> -	return generic_copy_file_range(file_in, pos_in, file_out, pos_out, len,
> -				       flags);
> -}
> -
>  /*
>   * Performs necessary checks before doing a file copy
>   *
> @@ -1440,6 +1418,24 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
>  	if (ret)
>  		return ret;
>  
> +	/*
> +	 * We allow some filesystems to handle cross sb copy, but passing
> +	 * a file of the wrong filesystem type to filesystem driver can result
> +	 * in an attempt to dereference the wrong type of ->private_data, so
> +	 * avoid doing that until we really have a good reason.
> +	 *
> +	 * nfs and cifs define several different file_system_type structures
> +	 * and several different sets of file_operations, but they all end up
> +	 * using the same ->copy_file_range() function pointer.
> +	 */
> +	if (file_out->f_op->copy_file_range) {
> +		if (file_in->f_op->copy_file_range !=
> +		    file_out->f_op->copy_file_range)
> +			return -EXDEV;
> +	} else if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb) {
> +		return -EXDEV;
> +	}
> +
>  	/* Don't touch certain kinds of inodes */
>  	if (IS_IMMUTABLE(inode_out))
>  		return -EPERM;
> @@ -1505,26 +1501,41 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>  	file_start_write(file_out);
>  
>  	/*
> -	 * Try cloning first, this is supported by more file systems, and
> -	 * more efficient if both clone and copy are supported (e.g. NFS).
> +	 * Cloning is supported by more file systems, so we implement copy on
> +	 * same sb using clone, but for filesystems where both clone and copy
> +	 * are supported (e.g. nfs,cifs), we only call the copy method.
>  	 */
> +	if (file_out->f_op->copy_file_range) {
> +		ret = file_out->f_op->copy_file_range(file_in, pos_in,
> +						      file_out, pos_out,
> +						      len, flags);
> +		goto done;
> +	}
> +
>  	if (file_in->f_op->remap_file_range &&
>  	    file_inode(file_in)->i_sb == file_inode(file_out)->i_sb) {
> -		loff_t cloned;
> -
> -		cloned = file_in->f_op->remap_file_range(file_in, pos_in,
> +		ret = file_in->f_op->remap_file_range(file_in, pos_in,
>  				file_out, pos_out,
>  				min_t(loff_t, MAX_RW_COUNT, len),
>  				REMAP_FILE_CAN_SHORTEN);
> -		if (cloned > 0) {
> -			ret = cloned;
> +		if (ret > 0)
>  			goto done;
> -		}
>  	}
>  
> -	ret = do_copy_file_range(file_in, pos_in, file_out, pos_out, len,
> -				flags);
> -	WARN_ON_ONCE(ret == -EOPNOTSUPP);
> +	/*
> +	 * We can get here for same sb copy of filesystems that do not implement
> +	 * ->copy_file_range() in case filesystem does not support clone or in
> +	 * case filesystem supports clone but rejected the clone request (e.g.
> +	 * because it was not block aligned).
> +	 *
> +	 * In both cases, fall back to kernel copy so we are able to maintain a
> +	 * consistent story about which filesystems support copy_file_range()
> +	 * and which filesystems do not, that will allow userspace tools to
> +	 * make consistent desicions w.r.t using copy_file_range().
> +	 */
> +	ret = generic_copy_file_range(file_in, pos_in, file_out, pos_out, len,
> +				      flags);
> +
>  done:
>  	if (ret > 0) {
>  		fsnotify_access(file_in);
> -- 
> 2.25.1
>