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From: Yonghong Song <yhs@fb.com>
To: <bpf@vger.kernel.org>
Cc: Alexei Starovoitov <ast@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>, <kernel-team@fb.com>
Subject: [PATCH bpf 1/2] bpf: fix a bug when getting subprog 0 jited image in check_attach_btf_id
Date: Wed, 4 Dec 2019 17:06:06 -0800
Message-ID: <20191205010606.177774-1-yhs@fb.com> (raw)
In-Reply-To: <20191205010606.177712-1-yhs@fb.com>

For jited bpf program, if the subprogram count is 1, i.e.,
there is no callees in the program, prog->aux->func will be NULL
and prog->bpf_func points to image address of the program.

If there is more than one subprogram, prog->aux->func is populated,
and subprogram 0 can be accessed through either prog->bpf_func or
prog->aux->func[0]. Other subprograms should be accessed through

This patch fixed a bug in check_attach_btf_id(), where
prog->aux->func[subprog_id] is used to access any subprogram which
caused a segfault like below:
  [79162.619208] BUG: kernel NULL pointer dereference, address:
  [79162.634255] Call Trace:
  [79162.634974]  ? _cond_resched+0x15/0x30
  [79162.635686]  ? kmem_cache_alloc_trace+0x162/0x220
  [79162.636398]  ? selinux_bpf_prog_alloc+0x1f/0x60
  [79162.637111]  bpf_prog_load+0x3de/0x690
  [79162.637809]  __do_sys_bpf+0x105/0x1740
  [79162.638488]  do_syscall_64+0x5b/0x180
  [79162.639147]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 5b92a28aae4d ("bpf: Support attaching tracing BPF program to other BPF programs")
Reported-by: Eelco Chaudron <echaudro@redhat.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
 kernel/bpf/verifier.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a0482e1c4a77..034ef81f935b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9636,7 +9636,10 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 				ret = -EINVAL;
 				goto out;
-			addr = (long) tgt_prog->aux->func[subprog]->bpf_func;
+			if (subprog == 0)
+				addr = (long) tgt_prog->bpf_func;
+			else
+				addr = (long) tgt_prog->aux->func[subprog]->bpf_func;
 		} else {
 			addr = kallsyms_lookup_name(tname);
 			if (!addr) {

  reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-05  1:06 [PATCH bpf 0/2] fix a verifier bug in check_attach_btf_id() Yonghong Song
2019-12-05  1:06 ` Yonghong Song [this message]
2019-12-05  5:33   ` [PATCH bpf 1/2] bpf: fix a bug when getting subprog 0 jited image in check_attach_btf_id Alexei Starovoitov
2019-12-05  1:06 ` [PATCH bpf 2/2] selftests/bpf: add a fexit/bpf2bpf test with target bpf prog no callees Yonghong Song
2019-12-05  5:37   ` Alexei Starovoitov

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