Commit 82e96972 authored May 04, 2018 by Martin KaFai Lau Committed by Daniel Borkmann May 09, 2018

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>

parent 53a7bdfb

kernel/bpf/btf.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}

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