The add_fd_from_fd_array() function takes a file descriptor as a parameter and tries to add either map or btf to the corresponding list of used objects. As was reported by Dan Carpenter, since the commit c81e4322acf0 ("bpf: Fix a potential use-after-free of BTF object"), the fdget() is called twice on the file descriptor, and thus userspace, potentially, can replace the file pointed to by the file descriptor in between the two calls. On practice, this shouldn't break anything on the kernel side, but for consistency fix the code such that only one fdget() is executed. Reported-by: Dan Carpenter Closes: https://lore.kernel.org/r/aY689z7gHNv8rgVO@stanley.mountain/ Fixes: c81e4322acf0 ("bpf: Fix a potential use-after-free of BTF object") Signed-off-by: Anton Protopopov --- kernel/bpf/verifier.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d4afd571761b..dbaafb64d3bd 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -25372,9 +25372,11 @@ static int add_fd_from_fd_array(struct bpf_verifier_env *env, int fd) return 0; } - btf = btf_get_by_fd(fd); - if (!IS_ERR(btf)) + btf = __btf_get_by_fd(f); + if (!IS_ERR(btf)) { + btf_get(btf); return __add_used_btf(env, btf); + } verbose(env, "fd %d is not pointing to valid bpf_map or btf\n", fd); return PTR_ERR(map); -- 2.34.1