[PATCH bpf v1 2/3] bpf: Don't reinit map value in prealloc_lru_pop

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

The LRU map that is preallocated may have its elements reused while
another program holds a pointer to it from bpf_map_lookup_elem. Hence,
only check_and_free_fields is appropriate when the element is being
deleted, as it ensures proper synchronization against concurrent access
of the map value. After that, we cannot call check_and_init_map_value
again as it may rewrite bpf_spin_lock, bpf_timer, and kptr fields while
they can be concurrently accessed from a BPF program.

Fixes: 68134668c17f ("bpf: Add map side support for bpf timers.")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/hashtab.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index da7578426a46..4d793a92301b 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -311,12 +311,8 @@ static struct htab_elem *prealloc_lru_pop(struct bpf_htab *htab, void *key,
 	struct htab_elem *l;
 
 	if (node) {
-		u32 key_size = htab->map.key_size;
-
 		l = container_of(node, struct htab_elem, lru_node);
-		memcpy(l->key, key, key_size);
-		check_and_init_map_value(&htab->map,
-					 l->key + round_up(key_size, 8));
+		memcpy(l->key, key, htab->map.key_size);
 		return l;
 	}
 
-- 
2.34.1