Request for cherry-picking overlayfs fixes in 5.10.x stable

Request for cherry-picking overlayfs fixes in 5.10.x stable

[Stan Hu]

A number of users have reported that under certain conditions using
the overlay filesystem, copy_file_range() can unexpectedly create a
0-byte file. [0]

This bug can cause significant problems because applications that copy
files expect the target file to match the source immediately after the
copy. After upgrading from Linux 5.4 to Linux 5.10, our Docker-based
CI tests started failing due to this bug, since Ruby's IO.copy_stream
uses this system call. We have worked around the problem by touching
the target file before using it, but this shouldn't be necessary.
Other projects, such as Rust, have added similar workarounds. [1]

As discussed in the linux-fsdevel mailing list [2], the bug appears to
be present in Linux 5.6 to 5.10, but not in Linux 5.11. We should be
able to cherry-pick the following upstream patches to fix this. Could
you cherry-pick them to 5.10.x stable? I've confirmed that these
patches, applied from top to bottom to that branch, pass the
reproduction test [3]:

82a763e61e2b601309d696d4fa514c77d64ee1be
9b91b6b019fda817eb52f728eb9c79b3579760bc

The diffstat:

 fs/overlayfs/file.c | 59
+++++++++++++++++++++++++++++++----------------------------
 1 file changed, 31 insertions(+), 28 deletions(-)

Note that these patches do not pick cleanly into 5.6.x - 5.9.x stable.

[0] https://github.com/docker/for-linux/issues/1015
[1] https://github.com/rust-lang/rust/blob/342db70ae4ecc3cd17e4fa6497f0a8d9534ccfeb/library/std/src/sys/unix/kernel_copy.rs#L565-L569
[2] https://marc.info/?l=linux-fsdevel&m=163847383311699&w=2
[3] https://github.com/docker/for-linux/issues/1015#issuecomment-841915668

Re: Request for cherry-picking overlayfs fixes in 5.10.x stable

[Greg KH]

On Thu, Dec 02, 2021 at 04:29:34PM -0800, Stan Hu wrote:
> A number of users have reported that under certain conditions using
> the overlay filesystem, copy_file_range() can unexpectedly create a
> 0-byte file. [0]
> 
> This bug can cause significant problems because applications that copy
> files expect the target file to match the source immediately after the
> copy. After upgrading from Linux 5.4 to Linux 5.10, our Docker-based
> CI tests started failing due to this bug, since Ruby's IO.copy_stream
> uses this system call. We have worked around the problem by touching
> the target file before using it, but this shouldn't be necessary.
> Other projects, such as Rust, have added similar workarounds. [1]
> 
> As discussed in the linux-fsdevel mailing list [2], the bug appears to
> be present in Linux 5.6 to 5.10, but not in Linux 5.11. We should be
> able to cherry-pick the following upstream patches to fix this. Could
> you cherry-pick them to 5.10.x stable? I've confirmed that these
> patches, applied from top to bottom to that branch, pass the
> reproduction test [3]:
> 
> 82a763e61e2b601309d696d4fa514c77d64ee1be
> 9b91b6b019fda817eb52f728eb9c79b3579760bc
> 
> The diffstat:
> 
>  fs/overlayfs/file.c | 59
> +++++++++++++++++++++++++++++++----------------------------
>  1 file changed, 31 insertions(+), 28 deletions(-)
> 
> Note that these patches do not pick cleanly into 5.6.x - 5.9.x stable.
> 
> [0] https://github.com/docker/for-linux/issues/1015
> [1] https://github.com/rust-lang/rust/blob/342db70ae4ecc3cd17e4fa6497f0a8d9534ccfeb/library/std/src/sys/unix/kernel_copy.rs#L565-L569
> [2] https://marc.info/?l=linux-fsdevel&m=163847383311699&w=2
> [3] https://github.com/docker/for-linux/issues/1015#issuecomment-841915668

Now queued up, thanks,

greg k-h