bpf: fix incorrect kmalloc usage in lpm_trie MAP_GET_NEXT_KEY rcu region

In commit b471f2f1de8b ("bpf: implement MAP_GET_NEXT_KEY command for LPM_TRIE map"),
the implemented MAP_GET_NEXT_KEY callback function is guarded with rcu read lock.
In the function body, "kmalloc(size, GFP_USER | __GFP_NOWARN)" is used which may
sleep and violate rcu read lock region requirements. This patch fixed the issue
by using GFP_ATOMIC instead to avoid blocking kmalloc. Tested with
CONFIG_DEBUG_ATOMIC_SLEEP=y as suggested by Eric Dumazet.

Fixes: b471f2f1de8b ("bpf: implement MAP_GET_NEXT_KEY command for LPM_TRIE map")
Signed-off-by: Yonghong Song <yhs@fb.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index d7ea962..8f083ea 100644 (file)
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -624,7 +624,7 @@ static int trie_get_next_key(struct bpf_map *map, void *_key, void *_next_key)
        }
 
        node_stack = kmalloc(trie->max_prefixlen * sizeof(struct lpm_trie_node *),
-                            GFP_USER | __GFP_NOWARN);
+                            GFP_ATOMIC | __GFP_NOWARN);
        if (!node_stack)
                return -ENOMEM;