bpf: Fix incorrect handling of user flags by percpu hash map updates

For BPF_MAP_TYPE_PERCPU_HASH and BPF_MAP_TYPE_LRU_PERCPU_HASH maps,
htab_map_check_update_flags() and check_flags() are not considering
the possibility of a combination of (BPF_NOEXIST, BPF_EXIST) flags
with (BPF_F_CPU, BPF_F_ALL_CPUS) flags. This causes the
(BPF_NOEXIST, BPF_EXIST) flags to lose their effect in some cases.

For example, when using (BPF_F_CPU | BPF_EXIST) or
(BPF_F_CPU | BPF_NOEXIST) flag combinations with bpf_map_update_elem()
on a percpu hash map, the BPF_EXIST flag does not prevent new
insertions as expected and BPF_NOEXIST flag does not prevent
modification of existing entries as expected.

This patch fixes the bug by adding proper flag validations and checks.
Before this patch, htab_map_check_update_flags() rejected
(BPF_F_ALL_CPUS | BPF_EXIST) and (BPF_F_ALL_CPUS | BPF_NOEXIST) with
-EINVAL. After the patch those combinations are accepted.

This patch also starts returning -EINVAL for (BPF_EXIST | BPF_NOEXIST),
with or without BPF_F_CPU, which was previously accepted.

Fixes: c6936161fd55 ("bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu_hash and lru_percpu_hash maps")
Signed-off-by: Masoud Aghasi <maghasi@disroot.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://patch.msgid.link/20261008120734.1565972-3-maghasi@disroot.org

1 files changed, 6 insertions, 4 deletions

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 66ebb5a32807..bf78e09f4d51 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -1367,11 +1367,11 @@ dec_count:
 static int check_flags(struct bpf_htab *htab, struct htab_elem *l_old,
 		       u64 map_flags)
 {
-	if (l_old && (map_flags & ~BPF_F_LOCK) == BPF_NOEXIST)
+	if (l_old && (map_flags & BPF_NOEXIST))
 		/* elem already exists */
 		return -EEXIST;
 
-	if (!l_old && (map_flags & ~BPF_F_LOCK) == BPF_EXIST)
+	if (!l_old && (map_flags & BPF_EXIST))
 		/* elem doesn't exist, cannot update it */
 		return -ENOENT;
 
@@ -1560,9 +1560,11 @@ err_lock_bucket:
 
 static int htab_map_check_update_flags(bool onallcpus, u64 map_flags)
 {
+	if (unlikely((map_flags & BPF_EXIST_FLAGS) == BPF_EXIST_FLAGS))
+		return -EINVAL;
 	if (unlikely(!onallcpus && map_flags > BPF_EXIST))
 		return -EINVAL;
-	if (unlikely(onallcpus && ((map_flags & BPF_F_LOCK) || (u32)map_flags > BPF_F_ALL_CPUS)))
+	if (unlikely(onallcpus && ((u32)map_flags & ~(BPF_EXIST_FLAGS | BPF_CPU_FLAGS))))
 		return -EINVAL;
 	return 0;
 }
@@ -1661,7 +1663,7 @@ static long __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
 	 * to remove older elem from htab and this removal
 	 * operation will need a bucket lock.
 	 */
-	if (map_flags != BPF_EXIST) {
+	if (!(map_flags & BPF_EXIST)) {
 		l_new = prealloc_lru_pop(htab, key, hash);
 		if (!l_new)
 			return -ENOMEM;