In the Linux kernel, the following vulnerability has been resolved: rhashtable: clear stale iter->p on table restart rhashtable_walk_start

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

rhashtable: clear stale iter->p on table restart

rhashtable_walk_start_check() 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.

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

Any caller that does multi-fragment rhashtable walks across
walk_stop/walk_start boundaries is affected. Concrete cases include
netlink_diag (__netlink_diag_dump in net/netlink/diag.c) and TIPC
(tipc_nl_sk_walk in net/tipc/socket.c).

Crash stack (netlink_diag):
BUG: KASAN: slab-use-after-free in rhashtable_walk_next+0x365/0x3c0
Read of size 8 at addr ffff88801a9d2438 (freed kmalloc-2k, offset 1080)
Call Trace:
rhashtable_walk_next+0x365/0x3c0 (lib/rhashtable.c:1016)
__netlink_diag_dump+0x160/0x760 (net/netlink/diag.c:122)
netlink_diag_dump+0xc2/0x240
netlink_dump+0x5bc/0x1270
netlink_recvmsg+0x7a3/0x980
sock_recvmsg+0x1bc/0x200
__sys_recvfrom+0x1d4/0x2c0