[PATCH bpf] bpf: fix an unitialized value in bpf_iter

From: Yonghong Song <yhs@fb.com>
To: <bpf@vger.kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>, <kernel-team@fb.com>,
	<syzbot+580f4f2a272e452d55cb@syzkaller.appspotmail.com>
Subject: [PATCH bpf] bpf: fix an unitialized value in bpf_iter
Date: Thu, 11 Feb 2021 16:59:26 -0800	[thread overview]
Message-ID: <20210212005926.2875002-1-yhs@fb.com> (raw)

Commit 15d83c4d7cef ("bpf: Allow loading of a bpf_iter program")
cached btf_id in struct bpf_iter_target_info so later on
if it can be checked cheaply compared to checking registered names.

syzbot found a bug that uninitialized value may occur to
bpf_iter_target_info->btf_id. This is because we allocated
bpf_iter_target_info structure with kmalloc and never initialized
field btf_id afterwards. This uninitialized btf_id is typically
compared to a u32 bpf program func proto btf_id, and the chance
of being equal is extremely slim.

This patch fixed the issue by using kzalloc which will also
prevent future likely instances due to adding new fields.

Reported-by: syzbot+580f4f2a272e452d55cb@syzkaller.appspotmail.com
Fixes: 15d83c4d7cef ("bpf: Allow loading of a bpf_iter program")
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 kernel/bpf/bpf_iter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 5454161407f1..a0d9eade9c80 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -287,7 +287,7 @@ int bpf_iter_reg_target(const struct bpf_iter_reg *reg_info)
 {
 	struct bpf_iter_target_info *tinfo;
 
-	tinfo = kmalloc(sizeof(*tinfo), GFP_KERNEL);
+	tinfo = kzalloc(sizeof(*tinfo), GFP_KERNEL);
 	if (!tinfo)
 		return -ENOMEM;
 
-- 
2.24.1

