From a2c86aa621c22f2a7e26c654f936d65cfff0aa91 Mon Sep 17 00:00:00 2001 From: KP Singh Date: Thu, 5 Feb 2026 08:07:55 +0100 Subject: [PATCH] bpf: Require frozen map for calculating map hash Currently, bpf_map_get_info_by_fd calculates and caches the hash of the map regardless of the map's frozen state. This leads to a TOCTOU bug where userspace can call BPF_OBJ_GET_INFO_BY_FD to cache the hash and then modify the map contents before freezing. Therefore, a trusted loader can be tricked into verifying the stale hash while loading the modified contents. Fix this by returning -EPERM if the map is not frozen when the hash is requested. This ensures the hash is only generated for the final, immutable state of the map. Fixes: ea2e6467ac36 ("bpf: Return hashes of maps in BPF_OBJ_GET_INFO_BY_FD") Reported-by: Toshi Piazza Signed-off-by: KP Singh Acked-by: Daniel Borkmann Link: https://lore.kernel.org/r/20260205070755.695776-1-kpsingh@kernel.org Signed-off-by: Alexei Starovoitov --- kernel/bpf/syscall.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 93bc0f4c65c57..683c332dbafbe 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -5328,6 +5328,9 @@ static int bpf_map_get_info_by_fd(struct file *file, if (info.hash_size != SHA256_DIGEST_SIZE) return -EINVAL; + if (!READ_ONCE(map->frozen)) + return -EPERM; + err = map->ops->map_get_hash(map, SHA256_DIGEST_SIZE, map->sha); if (err != 0) return err; -- 2.47.3