bpf: btf: Avoid WARN_ON when CONFIG_REFCOUNT_FULL=y

If CONFIG_REFCOUNT_FULL=y, refcount_inc() WARN when refcount is 0.
When creating a new btf, the initial btf->refcnt is 0 and
triggered the following:

[   34.855452] refcount_t: increment on 0; use-after-free.
[   34.856252] WARNING: CPU: 6 PID: 1857 at lib/refcount.c:153 refcount_inc+0x26/0x30
....
[   34.868809] Call Trace:
[   34.869168]  btf_new_fd+0x1af6/0x24d0
[   34.869645]  ? btf_type_seq_show+0x200/0x200
[   34.870212]  ? lock_acquire+0x3b0/0x3b0
[   34.870726]  ? security_capable+0x54/0x90
[   34.871247]  __x64_sys_bpf+0x1b2/0x310
[   34.871761]  ? __ia32_sys_bpf+0x310/0x310
[   34.872285]  ? bad_area_access_error+0x310/0x310
[   34.872894]  do_syscall_64+0x95/0x3f0

This patch uses refcount_set() instead.

Reported-by: Yonghong Song <yhs@fb.com>
Tested-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 22e1046a1a86ae1740e277eedf9292386283b237..fa0dce0452e740b9758748d94903a36bd3c820dd 100644 (file)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -1977,7 +1977,7 @@ static struct btf *btf_parse(void __user *btf_data, u32 btf_data_size,
 
        if (!err) {
                btf_verifier_env_free(env);
-               btf_get(btf);
+               refcount_set(&btf->refcnt, 1);
                return btf;
        }