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Shigeru Yoshida bbf4a17ad9 ipv6: Fix ECMP sibling count mismatch when clearing RTF_ADDRCONF
syzbot reported a kernel BUG in fib6_add_rt2node() when adding an IPv6
route. [0]

Commit f72514b3c5 ("ipv6: clear RA flags when adding a static
route") introduced logic to clear RTF_ADDRCONF from existing routes
when a static route with the same nexthop is added. However, this
causes a problem when the existing route has a gateway.

When RTF_ADDRCONF is cleared from a route that has a gateway, that
route becomes eligible for ECMP, i.e. rt6_qualify_for_ecmp() returns
true. The issue is that this route was never added to the
fib6_siblings list.

This leads to a mismatch between the following counts:

- The sibling count computed by iterating fib6_next chain, which
  includes the newly ECMP-eligible route

- The actual siblings in fib6_siblings list, which does not include
  that route

When a subsequent ECMP route is added, fib6_add_rt2node() hits
BUG_ON(sibling->fib6_nsiblings != rt->fib6_nsiblings) because the
counts don't match.

Fix this by only clearing RTF_ADDRCONF when the existing route does
not have a gateway. Routes without a gateway cannot qualify for ECMP
anyway (rt6_qualify_for_ecmp() requires fib_nh_gw_family), so clearing
RTF_ADDRCONF on them is safe and matches the original intent of the
commit.

[0]:
kernel BUG at net/ipv6/ip6_fib.c:1217!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 6010 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:fib6_add_rt2node+0x3433/0x3470 net/ipv6/ip6_fib.c:1217
[...]
Call Trace:
 <TASK>
 fib6_add+0x8da/0x18a0 net/ipv6/ip6_fib.c:1532
 __ip6_ins_rt net/ipv6/route.c:1351 [inline]
 ip6_route_add+0xde/0x1b0 net/ipv6/route.c:3946
 ipv6_route_ioctl+0x35c/0x480 net/ipv6/route.c:4571
 inet6_ioctl+0x219/0x280 net/ipv6/af_inet6.c:577
 sock_do_ioctl+0xdc/0x300 net/socket.c:1245
 sock_ioctl+0x576/0x790 net/socket.c:1366
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: f72514b3c5 ("ipv6: clear RA flags when adding a static route")
Reported-by: syzbot+cb809def1baaac68ab92@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=cb809def1baaac68ab92
Tested-by: syzbot+cb809def1baaac68ab92@syzkaller.appspotmail.com
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Link: https://patch.msgid.link/20260204095837.1285552-1-syoshida@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2026-02-05 08:38:40 -08:00
Documentation Pin control fixes for the v6.19 series: 2026-01-28 08:03:11 -08:00
LICENSES
arch Pin control fixes for the v6.19 series: 2026-01-28 08:03:11 -08:00
block block-6.19-20260122 2026-01-23 12:53:56 -08:00
certs
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-01-20 14:38:48 +08:00
drivers Two last-minute iwlwifi fixes: 2026-02-04 20:29:53 -08:00
fs for-6.19-rc7-tag 2026-01-29 09:07:17 -08:00
include net: add skb_header_pointer_careful() helper 2026-01-29 18:25:22 -08:00
init Significant patch series in this pull request: 2025-12-06 14:01:20 -08:00
io_uring io_uring-6.19-20260122 2026-01-23 12:51:00 -08:00
ipc Significant patch series in this pull request: 2025-12-06 14:01:20 -08:00
kernel tracing fixes for v6.19: 2026-01-24 17:18:57 -08:00
lib lib/buildid: use __kernel_read() for sleepable context 2026-01-14 22:16:21 -08:00
mm slab fix for 6.19-rc7 2026-01-21 09:19:15 -08:00
net ipv6: Fix ECMP sibling count mismatch when clearing RTF_ADDRCONF 2026-02-05 08:38:40 -08:00
rust Driver core fixes for 6.19-rc7 2026-01-24 10:13:22 -08:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2025-12-31 15:19:25 +08:00
scripts tracing fixes for v6.19: 2026-01-24 17:18:57 -08:00
security keys/trusted_keys: fix handle passed to tpm_buf_append_name during unseal 2026-01-25 19:03:45 +02:00
sound ALSA: hda/realtek: ALC269 fixup for Lenovo Yoga Book 9i 13IRU8 audio 2026-01-22 13:33:41 +01:00
tools selftest: net: add a test-case for encap segmentation after GRO 2026-02-03 19:23:41 -08:00
usr initramfs: add gen_init_cpio to hostprogs unconditionally 2025-11-26 21:55:40 +01:00
virt KVM fixes for 6.19-rc1 2025-12-18 18:38:45 +01:00
.clang-format s390/pci: Fix cyclic dead-lock in zpci_zdev_put() and zpci_scan_devices() 2025-12-14 11:03:58 +01:00
.clippy.toml
.cocciconfig
.editorconfig
.get_maintainer.ignore
.gitattributes
.gitignore rust: kbuild: add proc macro library support 2025-11-24 17:15:36 +01:00
.mailmap soc: fixes for 6.19, part 2 2026-01-21 09:34:45 -08:00
.pylintrc
.rustfmt.toml
COPYING
CREDITS nfc: MAINTAINERS: Orphan the NFC and look for new maintainers 2026-01-20 16:05:38 -08:00
Kbuild
Kconfig
MAINTAINERS MAINTAINERS: add an entry for PSP 2026-01-29 17:26:27 -08:00
Makefile Linux 6.19-rc7 2026-01-25 14:11:24 -08:00
README README: restructure with role-based documentation and guidelines 2025-11-29 08:40:33 -07:00

README

Linux kernel
============

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst



Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst