Re: [PATCH v3] lib/rhashtable: clear stale iter->p on table restart

[Herbert Xu]

On Tue, Jul 07, 2026 at 12:41:15PM -0400, Cen Zhang (Microsoft) wrote:
> 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
> 
> Fixes: 5d240a8936f6 ("rhashtable: improve rhashtable_walk stability when
> stop/start used.")
> Reported-by: AutonomousCodeSecurity@xxxxxxxxxxxxx
> Closes: https://lore.kernel.org/linux-crypto/CAB8m9Wh559e+=n8z51gB8DrbEyCc2mc0MgGjrRR6_VXBmU=2AQ@xxxxxxxxxxxxxx
> Signed-off-by: Cen Zhang (Microsoft) <blbllhy@xxxxxxxxx>
> ---
> v3: Solved patch format issue
> v2: Fix commit subject in Fixes tag
> Link: https://lore.kernel.org/linux-crypto/CAB8m9Wh559e+=n8z51gB8DrbEyCc2mc0MgGjrRR6_VXBmU=2AQ@xxxxxxxxxxxxxx
> 
>  lib/rhashtable.c | 1 +
>  1 file changed, 1 insertion(+)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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