Messages in this thread | | | Subject | Re: [PATCH v8] vfs: fix copy_file_range regression in cross-fs copies | From | dai.ngo@oracle ... | Date | Tue, 23 Feb 2021 07:29:09 -0800 |
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On 2/23/21 2:32 AM, Luis Henriques wrote: > On Mon, Feb 22, 2021 at 08:25:27AM -0800, dai.ngo@oracle.com 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@chromium.org/__;!!GqivPVa7Brio!P1UWThiSkxbjfjFQWNYJmCxGEkiLFyvHjH6cS-G1ZTt1z-TeqwGQgQmi49dC6w$ >>> Link: https://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/CANMq1KDZuxir2LM5jOTm0xx*BnvW=ZmpsG47CyHFJwnw7zSX6Q@mail.gmail.com/__;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@chromium.org> >>> Signed-off-by: Luis Henriques <lhenriques@suse.de> >>> --- >>> 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).
> > 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);
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