Hi In Debian Roland Clobus reported a regression with setting up loop devices from a backing squashfs file lying on read-only mounted target directory from a iso.
The original report is at: https://bugs.debian.org/1106070 Quoting the report: On Mon, May 19, 2025 at 12:15:10PM +0200, Roland Clobus wrote: > Package: linux-image-6.12.29-amd64 > Version: 6.12.29-1 > Severity: important > X-Debbugs-Cc: debian-am...@lists.debian.org > User: debian-am...@lists.debian.org > Usertags: amd64 > X-Debbugs-Cc: p...@hands.com > User: debian...@lists.debian.org > Usertags: openqa > X-Debbugs-Cc: debian-boot > > Hello maintainers of the kernel, > > The new kernel (6.12.29) has a modified behaviour (compared to 6.12.27) for > the loop device. > > This causes the Debian live images (for sid) to fail to boot. > > The change happened between 20250518T201633Z and 20250519T021902Z, which > matches the upload of 6.12.29 > (https://tracker.debian.org/news/1646619/accepted-linux-signed-amd64-612291-source-into-unstable/) > at 20250518T230426Z. > > To reproduce: > * Download the daily live image from > https://openqa.debian.net/tests/396941/asset/iso/smallest-build_sid_20250519T021902Z.iso > * Boot into the live image (the first boot option) > * Result: an initramfs shell (instead of a live system) -> FAIL > * Try: `losetup -r /dev/loop1 /run/live/medium/live/filesystem.squashfs` > * Result: `failed to set up loop device: invalid argument` -> FAIL > * Try: `cp /run/live/medium/live/filesystem.squashfs /` > * Try: `losetup -r /dev/loop2 /filesystem.squashfs` > * Result: `loop2: detected capacity change from 0 to 1460312` -> PASS > > It appears that the loopback device cannot be used any more with the mount > /run/live/medium (which is on /dev/sr0). > > I've verified: the md5sum of the squashfs file is OK. > > The newer kernel is not in trixie yet. > > With kind regards, > Roland Clobus A short reproducer is as follows: iso="netinst.iso" url="https://openqa.debian.net/tests/396941/asset/iso/smallest-build_sid_20250519T021902Z.iso"; if [ ! -e "${iso}" ]; then wget "${url}" -O "${iso}" fi mountdir="$(mktemp -d)" mount -v "./${iso}" "${mountdir}" losetup -v -r -f "${mountdir}/live/filesystem.squashfs" loosetup -l resulting in: mount: /tmp/tmp.HgbNe7ek3h: WARNING: source write-protected, mounted read-only. mount: /dev/loop0 mounted on /tmp/tmp.HgbNe7ek3h. losetup: /tmp/tmp.HgbNe7ek3h/live/filesystem.squashfs: failed to set up loop device: Invalid argument NAME SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE DIO LOG-SEC /dev/loop0 0 0 1 0 /root/netinst.iso 0 512 Reverting 184b147b9f7f ("loop: Add sanity check for read/write_iter") on top of 6.12.29 fixes the issue: mount: /tmp/tmp.ACkkdCdYvB: WARNING: source write-protected, mounted read-only. mount: /dev/loop0 mounted on /tmp/tmp.ACkkdCdYvB. NAME SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE DIO LOG-SEC /dev/loop1 0 0 0 1 /tmp/tmp.ACkkdCdYvB/live/filesystem.squashfs 0 512 /dev/loop0 0 0 1 0 /root/netinst.iso 0 512 For completeness, netinst.iso is a iso9660 fstype with mount options "ro,relatime,nojoliet,check=s,map=n,blocksize=2048,iocharset=utf8". #regzbot introduced: 184b147b9f7f #regzbot link: https://bugs.debian.org/1106070 Regards, Salvatore
