August 2026 - Libguestfs - libguestfs List Archives

Re: Can't boot UEFI VM after migration: "error: can't find command `linux16`"
by Srihari Parimi 07 Sep '26

07 Sep '26

Hi Richard, This is a more comprehensive description of the problem, where I respond to the specific issue and questions that you brought up during the discussion last week. I also cover the proposed solution towards the end. Kindly bear with the somewhat longish one - *[Comment 1] - Specific behaviors of the GRUB bootloader when encountering "Linux 16" versus "Linux EFI" directives.* - linux16 - Directive in GRUB boot loader to load the Linux Kernel image. It is documented in the GNU GRUB documentation - linux16 <https://doc.guix.gnu.org/grub/latest/en/grub.html#linux16> - The linux16 command forces GRUB load Linux Kernel image by using legacy *16-bit real-mode boot protocol*. - GRUB hands control to the kernel *while the CPU is still in 16-bit Real Mode*. - This allows the kernel's real-mode setup code to perform early hardware initialization using BIOS services (e.g., querying video modes, memory map)" - The Linux Kernel switches itself into 32-bit protected mode. - initrd16 loads the initramfs and is paired with linux16 - linuxefi - downstream GRUB2 bootloader directives specific to RHEL 7 for UEFI systems. Documented in RHEL 7 System Administrator Guide <https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/sy…> - Directive specific to RHEL 7. These directives are deprecated in RHEL 8 upwards which use standard GRUB directives linux, initrd instead and these work uniformly across BIOS or UEFI systems. - linuxefi and initrdefi directives use UEFI boot services to load the Linux Kernel image and initramfs respectively. - Based on the boot mode of the system - These GRUB configuration files are created using scripts in /etc/grub.d/ - primary script which generates the kernel image, initramfs boot loader commands is /etc/grub.d/10_linux. - RHEL 7.9 VM in BIOS Mode - GRUB reads the file /boot/grub2/grub.cfg which has the directives {linux16, initrd16} [root@localhost ~]# cat /boot/grub2/grub.cfg | egrep "linux16|initrd16" *linux16* /vmlinuz-3.10.0-1160.el7.x86_64 root=UUID=b635e330-0173-4866-9e5e-693086760507 ro crashkernel=auto rhgb quiet LANG=en_US.UTF-8 *initrd16* /initramfs-3.10.0-1160.el7.x86_64.img *linux16* /vmlinuz-0-rescue-bb246b817b814a44b5e960404fdc7ae3 root=UUID=b635e330-0173-4866 -9e5e-693086760507 ro crashkernel=auto rhgb quiet *initrd16* /initramfs-0-rescue-bb246b817b814a44b5e960404fdc7ae3.img - RHEL 7.9 VM in UEFI Mode - GRUB reads the file /boot/efi/EFI/redhat/grub.cfg which has the directives {linux16, initrd16} [root@localhost ~]# cat /boot/efi/EFI/redhat/grub.cfg | egrep "linuxefi|initrdefi" *linuxefi* /vmlinuz-3.10.0-1160.el7.x86_64 root=/dev/mapper/rhel-root ro crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet *initrdefi* /initramfs-3.10.0-1160.el7.x86_64.img *linuxefi* /vmlinuz-0-rescue-6e4e30972e924630b169d78059b932d2 root=/dev/mapper/rhel-root ro crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet *initrdefi* /initramfs-0-rescue-6e4e30972e924630b169d78059b932d2.img - Code snippet from /etc/grub.d/10_linux for RHEL9 and RHEL7. The root device UUID passed to the kernel (e.g., root=UUID=...) is dynamically queried and formatted by helper routines in /usr/share/grub/grub-mkconfig_lib using grub-probe . - Code snippet from */etc/grub.d/10_linux in RHEL9* if [ -d /sys/firmware/efi ]; then bootefi_device="`${grub_probe} --target=device /boot/efi/`" prepare_grub_to_access_device_with_variable boot ${bootefi_device} else boot_device="`${grub_probe} --target=device /boot/`" prepare_grub_to_access_device_with_variable boot ${boot_device} fi - Code snippet from */etc/grub.d/10_linux in RHEL7* if [ -d /sys/firmware/efi ]; then sed "s/^/$submenu_indentation/" << EOF ${linuxefi} ${rel_dirname}/${basename} root=${linux_root_device_thisversion} ro ${args} EOF else sed "s/^/$submenu_indentation/" << EOF linux${sixteenbit} ${rel_dirname}/${basename} root=${linux_root_device_thisversion} ro ${args} EOF fi - *[Comment 2] Confirming that the virtual machine Linux file format is fully compatible with the new directive* - Based on the analysis done for the previous comment, we can safely conclude that this problem is very specific to RHEL 7 only. Further, the problem occurs when following conditions are met - Source VM must be in UEFI boot mode - In the /etc/fstab, the /boot and /boot/efi partitions must be identified by the corresponding /dev/sd* files instead of the UUIDs (default) generated during FS creation. - The second condition forces virt-v2v conversion to configure GRUB. - As the grub configuration executes in context of libguestfs appliance (BIOS mode), it is generated with linux16, initrd16 whereas the VM is configured to boot in UEFI. - The VM powers up with UEFI firmware, but the linux16 directive switches the CPU into 16-bit real mode and look for BIOS services (/boot/grub2/i386-pc) which are absent. - *[Comment 3] Regarding the potential modification of file system table entries and disk device naming conventions, Richard Jones insisted that any statements regarding potential disk access problems must be accompanied by a detailed explanation of the "why" and "what" behind those risks* - The kernel device discovery (names /dev/sd*) is non-deterministic as it is based on order of driver initialization at the boot time. The order variation is due to asynchronous driver probe, kernel update or VM configuration changes. - By "hard-coding" the device names inside /etc/fstab, there could be a possibility of an unintended device being mounted onto an incorrect mount point, thus causing the system to fail or corrupt. - UUIDs (written into FS) are more reliable - where order of initialization would not matter making it more deterministic. - *The proposed solution* - Convert the references to /dev/sd* files to corresponding FS UUIDs *[Implemented and tested]* - Following change applicable only if OS is RHEL 7 and Boot mode is UEFI - Replace {linux16, initrd16} with {linuxefi, initrdefi} *[Work in progress to change from using sed to using APIs]* Thanks Srihari

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nbdkit | Failed pipeline for master | ecf13337
by GitLab 30 Aug '26

30 Aug '26

Pipeline #2803271110 has failed! Project: nbdkit ( https://gitlab.com/nbdkit/nbdkit ) Branch: master ( https://gitlab.com/nbdkit/nbdkit/-/commits/master ) Commit: ecf13337 ( https://gitlab.com/nbdkit/nbdkit/-/commit/ecf13337b1546b2a4ae88d8f10741b970… ) Commit Message: golang: Define "FUA requests" in man page Link... Commit Author: Richard W_M_ Jones ( https://gitlab.com/rwmjones ) Pipeline #2803271110 ( https://gitlab.com/nbdkit/nbdkit/-/pipelines/2803271110 ) triggered by Richard W_M_ Jones ( https://gitlab.com/rwmjones ) had 1 failed job. Job #16190445871 ( https://gitlab.com/nbdkit/nbdkit/-/jobs/16190445871/raw ) Stage: builds Name: x86_64-fedora-43 -- You're receiving this email because of your account on gitlab.com.

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nbdkit | Failed pipeline for master | a860c228
by GitLab 30 Aug '26

30 Aug '26

Pipeline #2803198717 has failed! Project: nbdkit ( https://gitlab.com/nbdkit/nbdkit ) Branch: master ( https://gitlab.com/nbdkit/nbdkit/-/commits/master ) Commit: a860c228 ( https://gitlab.com/nbdkit/nbdkit/-/commit/a860c228b0f4d8e8243c95cf1395f63fc… ) Commit Message: golang: Implement binding for nbdkit_name Commit Author: Richard W_M_ Jones ( https://gitlab.com/rwmjones ) Pipeline #2803198717 ( https://gitlab.com/nbdkit/nbdkit/-/pipelines/2803198717 ) triggered by Richard W_M_ Jones ( https://gitlab.com/rwmjones ) had 1 failed job. Job #16190086777 ( https://gitlab.com/nbdkit/nbdkit/-/jobs/16190086777/raw ) Stage: builds Name: x86_64-debian-12 -- You're receiving this email because of your account on gitlab.com.

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nbdkit | Failed pipeline for master | 97273a96
by GitLab 30 Aug '26

30 Aug '26

Pipeline #2803165170 has failed! Project: nbdkit ( https://gitlab.com/nbdkit/nbdkit ) Branch: master ( https://gitlab.com/nbdkit/nbdkit/-/commits/master ) Commit: 97273a96 ( https://gitlab.com/nbdkit/nbdkit/-/commit/97273a96281a32d01b1e63f29f33a5cc5… ) Commit Message: golang: Implement binding for nbdkit_export_name Commit Author: Richard W_M_ Jones ( https://gitlab.com/rwmjones ) Pipeline #2803165170 ( https://gitlab.com/nbdkit/nbdkit/-/pipelines/2803165170 ) triggered by Richard W_M_ Jones ( https://gitlab.com/rwmjones ) had 1 failed job. Job #16189926448 ( https://gitlab.com/nbdkit/nbdkit/-/jobs/16189926448/raw ) Stage: builds Name: x86_64-debian-12 -- You're receiving this email because of your account on gitlab.com.

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nbdkit | Failed pipeline for master | 22303839
by GitLab 28 Aug '26

28 Aug '26

Pipeline #2798950909 has failed! Project: nbdkit ( https://gitlab.com/nbdkit/nbdkit ) Branch: master ( https://gitlab.com/nbdkit/nbdkit/-/commits/master ) Commit: 22303839 ( https://gitlab.com/nbdkit/nbdkit/-/commit/223038393df287775485aa20b4c808d25… ) Commit Message: Merge branch 'golang-read-password' into 'maste... Commit Author: Richard W_M_ Jones ( https://gitlab.com/rwmjones ) Pipeline #2798950909 ( https://gitlab.com/nbdkit/nbdkit/-/pipelines/2798950909 ) triggered by Richard W_M_ Jones ( https://gitlab.com/rwmjones ) had 1 failed job. Job #16163967230 ( https://gitlab.com/nbdkit/nbdkit/-/jobs/16163967230/raw ) Stage: builds Name: x86_64-debian-13 -- You're receiving this email because of your account on gitlab.com.

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Fwd: Security Vulnerability in nbdkit QCOW2 ZSTD Decompression
by Richard W.M. Jones 24 Aug '26

24 Aug '26

----- Forwarded message from Tristan <TristanInSec(a)gmail.com> ----- Date: Mon, 24 Aug 2026 10:33:21 +0200 From: Tristan <TristanInSec(a)gmail.com> To: rjones(a)redhat.com Subject: Security Vulnerability in nbdkit QCOW2 ZSTD Decompression Hello, I am writing to report a security vulnerability in nbdkit's qcow2dec filter, confirmed at HEAD (commit 053f5a3). Summary of findings: ZSTD decompression heap over-read via incorrect buffer size (CVSS 6.5) The zstd_compressed_cluster() function sets the ZSTD input buffer size to cluster_size (uncompressed size) instead of compressed_size (actual allocation size). The equivalent zlib path correctly uses compressed_size, confirming this is a copy-paste bug. In worst case (2MB clusters, 512-byte compressed), this causes a 2MB over-read past a 512-byte allocation. The finding detail is attached. I would appreciate an acknowledgment of receipt. Thank you and please let me know if you need anything else. Regards, Tristan ================================================================= Heap Over-Read in ZSTD Decompression of QCOW2 Compressed Clusters ================================================================= CVSS 3.1: 6.5 (AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H) CWE: CWE-125 (Out-of-bounds Read) Auth: None (malicious QCOW2 file) Version: nbdkit 1.42.3, commit 053f5a3 (HEAD, 2026-07-21) File: filters/qcow2dec/qcow2dec.c, zstd_compressed_cluster(), line 712 Root Cause: The ZSTD input buffer size is set to cluster_size (the uncompressed cluster size) instead of compressed_size (the actual allocated buffer size). The equivalent zlib/deflate path correctly uses compressed_size. ZSTD path (INCORRECT) -- line 710-712: ZSTD_outBuffer out = { .dst = buf, .size = cluster_size, .pos = 0 }; ZSTD_inBuffer in = { .src = compressed_cluster, .size = cluster_size, .pos = 0 }; // ^^^^^^^^^^^^ // BUG: should be compressed_size zlib/deflate path (CORRECT) -- line 664-665: strm.next_in = (void *) compressed_cluster; strm.avail_in = compressed_size; // ^^^^^^^^^^^^^^^ correct: uses actual buffer size Buffer allocation -- line 840: compressed_cluster = malloc(compressed_size); Data Flow: 1. qcow2dec filter parses QCOW2 image with ZSTD-compressed clusters 2. L2 entry encodes nr_sectors (line 789), minimum 1 sector (512 bytes) 3. compressed_size = nr_sectors * 512 (line 806) 4. malloc(compressed_size) allocates buffer (line 840) 5. ZSTD input buffer declares .size = cluster_size (line 712) 6. ZSTD_decompressStream() may read up to cluster_size bytes 7. Over-read: cluster_size - compressed_size bytes past allocation Worst Case: cluster_bits=21 (2 MB clusters), single-sector compressed data: - compressed_size = 512 bytes - cluster_size = 2,097,152 bytes - Over-read: up to 2,096,640 bytes past the 512-byte allocation Impact: Crash (DoS) when serving a crafted QCOW2 image via nbdkit. In cloud and virtualization environments where untrusted disk images are served, an attacker can trigger this by providing a crafted QCOW2 image with ZSTD-compressed clusters. Potential heap data disclosure if the process survives the over-read. Fix: Change line 712 from: { .src = compressed_cluster, .size = cluster_size, .pos = 0 }; to: { .src = compressed_cluster, .size = compressed_size, .pos = 0 }; ----- End forwarded message ----- -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-builder quickly builds VMs from scratch http://libguestfs.org/virt-builder.1.html

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Re: [RFC PATCH guestfs-tools] builder: templates: Add Ubuntu 24.04 cloud image support
by Aravind Sivamani (asivaman) 12 Aug '26

12 Aug '26

Hi Richard, hi all, I am following up on this RFC The implementation is now ready for review in guestfs-tools PR #51: https://github.com/libguestfs/guestfs-tools/pull/51 It is rebased onto the current master. End-to-end Noble template generation, focused tests, image checks, and native-size BIOS/UEFI boots passed locally. The exact virt-builder ubuntu-24.04 --size 6G flow also completes and boots under UEFI; resized legacy-BIOS boot remains an open item documented in the PR. The Fedora workflow is waiting for first-time-contributor approval, so CI has not run yet. Richard, when you have a chance, could you please review the pinned, checksum-verified Canonical image approach and approve the workflow so CI can begin? Thanks, Aravind [Cisco Midnight Blue v1]<https://www.cisco.com/> Aravind Sivamani Software Engineer asivaman(a)cisco.com<mailto:asivaman@cisco.com> Phone: +1 984 999 1776 [cid:a530ddc6-4317-4b32-9b0f-18c68e49e229]<https://www.linkedin.com/in/aravind-sivamani> Cisco Systems NSO Packages and Tooling Services Sveavagen 25 Stockholm Sweden This email may contain confidential and privileged material for the sole use of the intended recipient. Any review, use, distribution or disclosure by others is strictly prohibited. If you are not the intended recipient (or authorized to receive for the recipient), please contact the sender by reply email and delete all copies of this message. Update Profile<https://www.cisco.com/c/en/us/about/help/login-account-help.html#~profile> - Privacy<https://www.cisco.com/c/en/us/about/legal/privacy-full.html> - Company Registration<http://www.cisco.com/c/en/us/about/legal/terms-sale-software-license-agreem…> ________________________________ From: Aravind Sivamani (asivaman) Sent: Tuesday, July 21, 2026 1:51 AM To: guestfs(a)lists.libguestfs.org <guestfs(a)lists.libguestfs.org> Cc: rjones(a)redhat.com <rjones(a)redhat.com> Subject: [RFC PATCH guestfs-tools] builder: templates: Add Ubuntu 24.04 cloud image support Hi all, I’m working on adding Ubuntu 24.04 (Noble) support to the virt-builder template generator, and I’d appreciate feedback on the proposed approach. Ubuntu 24.04 no longer publishes the Debian Installer tree used by the existing virt-install/preseed path. This RFC imports a dated Canonical Noble cloud image, verifies its pinned SHA-256, converts it to raw, and then reuses the existing inspection, sysprep, compression, and index-generation stages. Existing installer-based templates remain unchanged. I tested this end to end on Ubuntu 24.04. The focused catalog/import tests, shell syntax, OCaml parsing, XZ integrity, and generated-index checks passed. The generated image had an empty machine ID, no SSH host keys or stale cloud-init state, and a locked root account. I have not run the full repository make check because this checkout lacked the generated Autotools bootstrap files. I’d especially appreciate your thoughts on: - Using a pinned dated image versus SimpleStreams - Preserving Noble’s native virtual size and cloud-init behavior - The expected BIOS/UEFI boot validation before publication Public branch: https://github.com/aravindsivamani/guestfs-tools/tree/ubuntu-24.04-cloud-im… The patch is attached. Thanks for taking a look! Best, Aravind [Cisco Midnight Blue v1]<https://www.cisco.com/> Aravind Sivamani Software Engineer asivaman(a)cisco.com<mailto:asivaman@cisco.com> Phone: +1 984 999 1776 [cid:0f519272-8687-4198-bbaf-78420df04f06]<https://www.linkedin.com/in/aravind-sivamani> Cisco Systems NSO Packages and Tooling Services Sveavagen 25 Stockholm Sweden This email may contain confidential and privileged material for the sole use of the intended recipient. Any review, use, distribution or disclosure by others is strictly prohibited. If you are not the intended recipient (or authorized to receive for the recipient), please contact the sender by reply email and delete all copies of this message. Update Profile<https://www.cisco.com/c/en/us/about/help/login-account-help.html#~profile> - Privacy<https://www.cisco.com/c/en/us/about/legal/privacy-full.html> - Company Registration<http://www.cisco.com/c/en/us/about/legal/terms-sale-software-license-agreem…>

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