CVE-2026-64563: rhashtable: clear stale iter->p on table restart

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

rhashtable: clear stale iter->p on table restart

rhashtablewalkstartcheck() has two restart paths when resuming a walk. When iter->walker.tbl is valid, it re-validates iter->p against the table and sets iter->p = NULL if the object is gone. When iter->walker.tbl is NULL (table was freed during resize), it resets slot and skip but forgets to clear iter->p.

rhashtablewalknext() then dereferences the stale iter->p, reading freed memory. This is a use-after-free.

Any caller that does multi-fragment rhashtable walks across walkstop/walkstart boundaries is affected. Concrete cases include netlinkdiag (netlinkdiagdump in net/netlink/diag.c) and TIPC (tipcnlskwalk in net/tipc/socket.c).

Crash stack (netlinkdiag): BUG: KASAN: slab-use-after-free in rhashtablewalknext+0x365/0x3c0 Read of size 8 at addr ffff88801a9d2438 (freed kmalloc-2k, offset 1080) Call Trace: rhashtablewalknext+0x365/0x3c0 (lib/rhashtable.c:1016) netlinkdiagdump+0x160/0x760 (net/netlink/diag.c:122) netlinkdiagdump+0xc2/0x240 netlinkdump+0x5bc/0x1270 netlinkrecvmsg+0x7a3/0x980 sockrecvmsg+0x1bc/0x200 sysrecvfrom+0x1d4/0x2c0