Re: [PATCH v3] SUNRPC/cache: Fix unsafe traverse caused double-free in cache_purge

[NeilBrown <neilb@suse.de>]

[-- Attachment #1: Type: text/plain, Size: 1473 bytes --]

On Mon, Apr 06 2020, Yihao Wu wrote:

> Deleting list entry within hlist_for_each_entry_safe is not safe unless
> next pointer (tmp) is protected too. It's not, because once hash_lock
> is released, cache_clean may delete the entry that tmp points to. Then
> cache_purge can walk to a deleted entry and tries to double free it.
>
> Fix this bug by holding only the deleted entry's reference.
>
> Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>
> ---
> v1->v2: Use Neil's better solution
> v2->v3: Fix a checkscript warning
>
>  net/sunrpc/cache.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index af0ddd28b081..b445874e8e2f 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -541,7 +541,9 @@ void cache_purge(struct cache_detail *detail)
>  	dprintk("RPC: %d entries in %s cache\n", detail->entries, detail->name);
>  	for (i = 0; i < detail->hash_size; i++) {
>  		head = &detail->hash_table[i];
> -		hlist_for_each_entry_safe(ch, tmp, head, cache_list) {
> +		while (!hlist_empty(head)) {
> +			ch = hlist_entry(head->first, struct cache_head,
> +					 cache_list);
>  			sunrpc_begin_cache_remove_entry(ch, detail);
>  			spin_unlock(&detail->hash_lock);
>  			sunrpc_end_cache_remove_entry(ch, detail);
> -- 
> 2.20.1.2432.ga663e714

Reviewed-by: NeilBrown <neilb@suse.de>

Thanks for finding the bug and testing the solution!
NeilBrown

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 832 bytes --]