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    Subject[PATCH AUTOSEL 5.6 14/79] SUNRPC/cache: Fix unsafe traverse caused double-free in cache_purge
    Date
    From: Yihao Wu <wuyihao@linux.alibaba.com>

    [ Upstream commit 43e33924c38e8faeb0c12035481cb150e602e39d ]

    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.

    Suggested-by: NeilBrown <neilb@suse.de>
    Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>
    Reviewed-by: NeilBrown <neilb@suse.de>
    [ cel: removed unused variable ]
    Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/sunrpc/cache.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
    index bd843a81afa0b..d36cea4e270de 100644
    --- a/net/sunrpc/cache.c
    +++ b/net/sunrpc/cache.c
    @@ -521,7 +521,6 @@ void cache_purge(struct cache_detail *detail)
    {
    struct cache_head *ch = NULL;
    struct hlist_head *head = NULL;
    - struct hlist_node *tmp = NULL;
    int i = 0;

    spin_lock(&detail->hash_lock);
    @@ -533,7 +532,9 @@ 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
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