diff mbox series

[v5] vfs: fix copy_file_range regression in cross-fs copies

Message ID 20210218151752.26710-1-lhenriques@suse.de (mailing list archive)
State New
Headers show
Series [v5] vfs: fix copy_file_range regression in cross-fs copies | expand

Commit Message

Luis Henriques Feb. 18, 2021, 3:17 p.m. UTC
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.

This patch restores some cross-filesystem copy restrictions that existed
prior to commit 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
devices").  Filesystems are still allowed to fall-back to the VFS
generic_copy_file_range() implementation, but that has now to be done
explicitly.

nfsd is also modified to fall-back into generic_copy_file_range() in case
vfs_copy_file_range() fails with -EOPNOTSUPP or -EXDEV.

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/
Reported-by: Nicolas Boichat <drinkcat@chromium.org>
Signed-off-by: Luis Henriques <lhenriques@suse.de>
---
And v5!  Sorry.  Sure, it makes sense to go through the all the vfs_cfr()
checks first.

Again, here's my request for testing.

Changes since v4
- nfsd falls-back to generic_copy_file_range() only *if* it gets -EOPNOTSUPP
  or -EXDEV.
Changes since v3
- dropped the COPY_FILE_SPLICE flag
- kept the f_op's checks early in generic_copy_file_checks, implementing
  Amir's suggestions
- modified nfsd to use generic_copy_file_range()
Changes since v2
- do all the required checks earlier, in generic_copy_file_checks(),
  adding new checks for ->remap_file_range
- new COPY_FILE_SPLICE flag
- don't remove filesystem's fallback to generic_copy_file_range()
- updated commit changelog (and subject)
Changes since v1 (after Amir review)
- restored do_copy_file_range() helper
- return -EOPNOTSUPP if fs doesn't implement CFR
- updated commit description
 fs/nfsd/vfs.c   |  8 +++++++-
 fs/read_write.c | 50 +++++++++++++++++++++++--------------------------
 2 files changed, 30 insertions(+), 28 deletions(-)

Comments

Amir Goldstein Feb. 18, 2021, 3:53 p.m. UTC | #1
On Thu, Feb 18, 2021 at 5:16 PM Luis Henriques <lhenriques@suse.de> 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.
>
> This patch restores some cross-filesystem copy restrictions that existed
> prior to commit 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
> devices").  Filesystems are still allowed to fall-back to the VFS
> generic_copy_file_range() implementation, but that has now to be done
> explicitly.
>
> nfsd is also modified to fall-back into generic_copy_file_range() in case
> vfs_copy_file_range() fails with -EOPNOTSUPP or -EXDEV.
>
> 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/
> Reported-by: Nicolas Boichat <drinkcat@chromium.org>
> Signed-off-by: Luis Henriques <lhenriques@suse.de>
> ---
> And v5!  Sorry.  Sure, it makes sense to go through the all the vfs_cfr()
> checks first.

You missed my other comment on v4...

not checking NULL copy_file_range case.

Thanks,
Amir.
Luis Henriques Feb. 18, 2021, 4:35 p.m. UTC | #2
Amir Goldstein <amir73il@gmail.com> writes:

> On Thu, Feb 18, 2021 at 5:16 PM Luis Henriques <lhenriques@suse.de> 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.
>>
>> This patch restores some cross-filesystem copy restrictions that existed
>> prior to commit 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
>> devices").  Filesystems are still allowed to fall-back to the VFS
>> generic_copy_file_range() implementation, but that has now to be done
>> explicitly.
>>
>> nfsd is also modified to fall-back into generic_copy_file_range() in case
>> vfs_copy_file_range() fails with -EOPNOTSUPP or -EXDEV.
>>
>> 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/
>> Reported-by: Nicolas Boichat <drinkcat@chromium.org>
>> Signed-off-by: Luis Henriques <lhenriques@suse.de>
>> ---
>> And v5!  Sorry.  Sure, it makes sense to go through the all the vfs_cfr()
>> checks first.
>
> You missed my other comment on v4...
>
> not checking NULL copy_file_range case.

Ah, yeah I did missed it.  I'll follow up with yet another revision.

Cheers,
diff mbox series

Patch

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 04937e51de56..23dab0fa9087 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -568,6 +568,7 @@  __be32 nfsd4_clone_file_range(struct nfsd_file *nf_src, u64 src_pos,
 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
@@ -578,7 +579,12 @@  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 75f764b43418..214d44f7cbfa 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1388,28 +1388,6 @@  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
  *
@@ -1427,6 +1405,25 @@  static int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
 	loff_t size_in;
 	int ret;
 
+	/*
+	 * 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) {
+		if (file_in->f_op->copy_file_range !=
+		    file_out->f_op->copy_file_range)
+			return -EXDEV;
+	} else if (file_in->f_op->remap_file_range) {
+		if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
+			return -EXDEV;
+	} else {
+                return -EOPNOTSUPP;
+	}
+
 	ret = generic_file_rw_checks(file_in, file_out);
 	if (ret)
 		return ret;
@@ -1499,8 +1496,7 @@  ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 	 * Try cloning first, this is supported by more file systems, and
 	 * more efficient if both clone and copy are supported (e.g. NFS).
 	 */
-	if (file_in->f_op->remap_file_range &&
-	    file_inode(file_in)->i_sb == file_inode(file_out)->i_sb) {
+	if (file_in->f_op->remap_file_range) {
 		loff_t cloned;
 
 		cloned = file_in->f_op->remap_file_range(file_in, pos_in,
@@ -1513,9 +1509,9 @@  ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 		}
 	}
 
-	ret = do_copy_file_range(file_in, pos_in, file_out, pos_out, len,
-				flags);
-	WARN_ON_ONCE(ret == -EOPNOTSUPP);
+	ret = file_out->f_op->copy_file_range(file_in, pos_in,
+					      file_out, pos_out,
+					      len, flags);
 done:
 	if (ret > 0) {
 		fsnotify_access(file_in);