Re: [PATCH v8] vfs: fix copy_file_range regression in cross-fs copies
From: dai . ngo
Date: Tue Feb 23 2021 - 11:06:09 EST
On 2/23/21 7:29 AM, dai.ngo@xxxxxxxxxx wrote:
On 2/23/21 2:32 AM, Luis Henriques wrote:
On Mon, Feb 22, 2021 at 08:25:27AM -0800, dai.ngo@xxxxxxxxxx wrote:
On 2/22/21 2:24 AM, Luis Henriques 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://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/20210212044405.4120619-1-drinkcat@xxxxxxxxxxxx/__;!!GqivPVa7Brio!P1UWThiSkxbjfjFQWNYJmCxGEkiLFyvHjH6cS-G1ZTt1z-TeqwGQgQmi49dC6w$
Link:
https://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/CANMq1KDZuxir2LM5jOTm0xx*BnvW=ZmpsG47CyHFJwnw7zSX6Q@xxxxxxxxxxxxxx/__;Kw!!GqivPVa7Brio!P1UWThiSkxbjfjFQWNYJmCxGEkiLFyvHjH6cS-G1ZTt1z-TeqwGQgQmgCmMHzA$
Link:
https://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/20210126135012.1.If45b7cdc3ff707bc1efa17f5366057d60603c45f@changeid/__;!!GqivPVa7Brio!P1UWThiSkxbjfjFQWNYJmCxGEkiLFyvHjH6cS-G1ZTt1z-TeqwGQgQmzqItkrQ$
Reported-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
Signed-off-by: Luis Henriques <lhenriques@xxxxxxx>
---
Changes since v7
- set 'ret' to '-EOPNOTSUPP' before the clone 'if' statement so
that the
error returned is always related to the 'copy' operation
Changes since v6
- restored i_sb checks for the clone operation
Changes since v5
- check if ->copy_file_range is NULL before calling it
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 | 49
++++++++++++++++++++++++-------------------------
2 files changed, 31 insertions(+), 26 deletions(-)
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..5a26297fd410 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;
I think this check is redundant, it's done in vfs_copy_file_range.
If this check is removed then the else clause below should be removed
also. Once this check and the else clause are removed then might as
well move the the check of copy_file_range from here to
vfs_copy_file_range.
I don't think it's really redundant, although I agree is messy due to
the
fact we try to clone first instead of copying them.
So, in the clone path, this is the only place where we return -EXDEV if:
1) we don't have ->copy_file_range *and*
2) we have ->remap_file_range but the i_sb are different.
The check in vfs_copy_file_range() is only executed if:
1) we have *valid* ->copy_file_range ops and/or
2) we have *valid* ->remap_file_range
So... if we remove the check in generic_copy_file_checks() as you
suggest
and:
- we don't have ->copy_file_range,
- we have ->remap_file_range but
- the i_sb are different
we'll return the -EOPNOTSUPP (the one set in line "ret =
-EOPNOTSUPP;" in
function vfs_copy_file_range() ) instead of -EXDEV.
Yes, this is the different.The NFS code handles both -EOPNOTSUPP and
-EXDEVV by doing generic_copy_file_range. Do any other consumers of
vfs_copy_file_range rely on -EXDEV and not -EOPNOTSUPP and which is
the correct error code for this case? It seems to me that -EOPNOTSUPP
is more appropriate than EXDEV when (sb1 != sb2).
So with the current patch, for a clone operation across 2 filesystems:
. if src and dst filesystem support both copy_file_range and
map_file_range then the code returns -ENOTSUPPORT.
. if the filesystems only support map_file_range then the
code returns -EXDEV
This seems confusing, shouldn't only 1 error code returned for this case?
-Dai
But I may have got it all wrong. I've looked so many times at this code
that I'm probably useless at finding problems in it :-)
You're not alone, we all try to do the right thing :-)
-Dai
Cheers,
--
Luís
-Dai
+ } else {
+ return -EOPNOTSUPP;
+ }
+
ret = generic_file_rw_checks(file_in, file_out);
if (ret)
return ret;
@@ -1495,6 +1492,7 @@ ssize_t vfs_copy_file_range(struct file
*file_in, loff_t pos_in,
file_start_write(file_out);
+ ret = -EOPNOTSUPP;
/*
* Try cloning first, this is supported by more file
systems, and
* more efficient if both clone and copy are supported (e.g.
NFS).
@@ -1513,9 +1511,10 @@ 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);
+ 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);
done:
if (ret > 0) {
fsnotify_access(file_in);