Public bug reported: Copied from https://lore.kernel.org/stable/CAMBWrQ=1mkxnmt_6jnqp_xxr7psvywpbjc6p1qcy9eny8rf...@mail.gmail.com/:
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 --- I reproduced this bug in Ubuntu 18.04: ``` # bash test.sh Sending build context to Docker daemon 43.05kB Step 1/2 : FROM debian:10.8-slim ---> 115566c891d1 Step 2/2 : RUN apt update && apt install -y gcc strace ---> Using cache ---> 0dfb7ffcd427 Successfully built 0dfb7ffcd427 Successfully tagged strace:latest Local: OK Docker - mounted: Copy failed Docker - copied: OK ``` ``` root@stanhu-ubuntu-18:/home/stanhu# lsb_release -rd Description: Ubuntu 18.04.6 LTS Release: 18.04 root@stanhu-ubuntu-18:/home/stanhu# uname -r 5.4.0-1057-gcp ``` Per [the latest update on the kernel stable mailing list](https://lore.kernel.org/stable/[email protected]), the kernel backport fix for 5.10 has been queued for review and should land in the [`stable-5.10.y` branch](https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/log/?h=linux-5.10.y) soon. To avoid this bug, I'd suggest avoid Linux v5.6.0 - v5.10.83 for now, unless you backport the two patches below: 1. https://github.com/torvalds/linux/commit/@82a763e61e2b601309d696d4fa514c77d64ee1be 1. https://github.com/torvalds/linux/commit/@9b91b6b019fda817eb52f728eb9c79b3579760bc I've confirmed that 5.5.19 does NOT have this bug, and it was introduced in 5.6.0 via https://github.com/torvalds/linux/commit/1a980b8cbf0059a5308eea61522f232fd03002e2. ** Affects: linux-base (Ubuntu) Importance: Undecided Status: New ** Package changed: linux (Ubuntu) => linux-base (Ubuntu) -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1953199 Title: 0-byte files created in overlay filesystem To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-base/+bug/1953199/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
