XPost: linux.debian.bugs.dist, linux.kernel
From: [email protected]

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: [email protected]
User: [email protected]
Usertags: amd64
X-Debbugs-Cc: [email protected]
User: [email protected]
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

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XPost: linux.debian.bugs.dist, linux.kernel
From: [email protected]

On Tue, May 20, 2025 at 07:57:31AM +0200, Salvatore Bonaccorso wrote:

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: [email protected]
User: [email protected]
Usertags: amd64
X-Debbugs-Cc: [email protected]
User: [email protected]
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

Just tested: The regression exists as well in 6.15-rc7 so it is not
specific to the stable 6.12.y update.

Regards,
Salvatore

--- SoupGate-Win32 v1.05
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XPost: linux.debian.bugs.dist, linux.kernel
From: [email protected]

Fixed here:

https://git.kernel.dk/cgit/linux/commit/?h=block-6.15&id=355341e4359b2d5edf0ed5e117f7e9e7a0a5dac0

and will land upstream this week.

--
Jens Axboe

--- SoupGate-Win32 v1.05
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XPost: linux.debian.bugs.dist, linux.kernel
From: [email protected]

Salvatore Bonaccorso <[email protected]> on Tue, 2025/05/20 07:57:

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

We are suffering the same for Arch Linux. Already reported here:

https://lore.kernel.org/all/[email protected]/
--
main(a){char*c=/* Schoene Gruesse */"B?IJj;MEH" "CX:;",b;for(a/* Best regards my address: */=0;b=c[a++];) putchar(b-1/(/* Chris cc -ox -xc - && ./x */b/42*2-3)*42);}

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