CVE-2026-74563: rds: tcp: hold the RCU lock across ipv6_chk_addr() in rds_tcp_laddr_check()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

rds: tcp: hold the RCU lock across ipv6_chk_addr() in rds_tcp_laddr_check()

rds_tcp_laddr_check() looks up a scoped IPv6 interface with
dev_get_by_index_rcu(), drops the RCU read-side lock, and only then
passes the bare struct net_device * into ipv6_chk_addr().

dev_get_by_index_rcu() only keeps the device alive within the same RCU
read-side section. After rcu_read_unlock(), a concurrent RTM_DELLINK can
free the net_device; ipv6_chk_addr() then dereferences the stale pointer
in __ipv6_chk_addr_and_flags() (e.g. l3mdev_master_dev_rcu(dev)), reading
freed memory.

Keep the RCU read-side lock held across the ipv6_chk_addr() call instead
of dropping it right after the lookup, so the device cannot be freed
while it is in use.

  BUG: KASAN: slab-use-after-free in __ipv6_chk_addr_and_flags (... net/ipv6/addrconf.c:1998)
  Read of size 8 at addr ffff8880106ec000 by task exploit/153
  Call Trace:
   ...
   kasan_report (mm/kasan/report.c:595)
   __ipv6_chk_addr_and_flags (... net/ipv6/addrconf.c:1998)
   ipv6_chk_addr (net/ipv6/addrconf.c:2031 net/ipv6/addrconf.c:1972)
   rds_tcp_laddr_check (net/rds/tcp.c:370)
   rds_bind (net/rds/bind.c:248)
   __sys_bind (net/socket.c:1920)
   __x64_sys_bind (net/socket.c:1956)
   do_syscall_64 (arch/x86/entry/syscall_64.c:63)
   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)

The Linux kernel CVE team has assigned CVE-2026-74563 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.19 with commit eee2fa6ab3225192d6d894c54a6fb02ac9efdff6 and fixed in 6.6.151 with commit 76dd48886eeeb5fcf2b837d2f4c3d17eebeac9ef
	Issue introduced in 4.19 with commit eee2fa6ab3225192d6d894c54a6fb02ac9efdff6 and fixed in 6.12.103 with commit f0d1fb05d70c8a561cd8d0473bcacafa2fc137ff
	Issue introduced in 4.19 with commit eee2fa6ab3225192d6d894c54a6fb02ac9efdff6 and fixed in 6.18.44 with commit b1d480fce05f857dc438080cd8c9244b84a83494
	Issue introduced in 4.19 with commit eee2fa6ab3225192d6d894c54a6fb02ac9efdff6 and fixed in 7.1.8 with commit 8398bc477d3cb3e2b018a5aaac2bec0f69acda30
	Issue introduced in 4.19 with commit eee2fa6ab3225192d6d894c54a6fb02ac9efdff6 and fixed in 7.2-rc6 with commit 78f75d632f74b8de0f081a128588f7c37d0d1164

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74563
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/rds/tcp.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/76dd48886eeeb5fcf2b837d2f4c3d17eebeac9ef
	https://git.kernel.org/stable/c/f0d1fb05d70c8a561cd8d0473bcacafa2fc137ff
	https://git.kernel.org/stable/c/b1d480fce05f857dc438080cd8c9244b84a83494
	https://git.kernel.org/stable/c/8398bc477d3cb3e2b018a5aaac2bec0f69acda30
	https://git.kernel.org/stable/c/78f75d632f74b8de0f081a128588f7c37d0d1164