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* [PATCH] bpf: btf: Fix a missing-check bug
@ 2018-10-19 22:29 Wenwen Wang
  2018-10-22 15:40 ` Martin Lau
  2018-10-22 15:57 ` Y Song
  0 siblings, 2 replies; 5+ messages in thread
From: Wenwen Wang @ 2018-10-19 22:29 UTC (permalink / raw)
  To: Wenwen Wang
  Cc: Kangjie Lu, Alexei Starovoitov, Daniel Borkmann,
	open list:BPF (Safe dynamic programs and tools),
	open list:BPF (Safe dynamic programs and tools)

In btf_parse(), the header of the user-space btf data 'btf_data' is firstly
parsed and verified through btf_parse_hdr(). In btf_parse_hdr(), the header
is copied from user-space 'btf_data' to kernel-space 'btf->hdr' and then
verified. If no error happens during the verification process, the whole
data of 'btf_data', including the header, is then copied to 'data' in
btf_parse(). It is obvious that the header is copied twice here. More
importantly, no check is enforced after the second copy to make sure the
headers obtained in these two copies are same. Given that 'btf_data'
resides in the user space, a malicious user can race to modify the header
between these two copies. By doing so, the user can inject inconsistent
data, which can cause undefined behavior of the kernel and introduce
potential security risk.

To avoid the above issue, this patch rewrites the header after the second
copy, using 'btf->hdr', which is obtained in the first copy.

Signed-off-by: Wenwen Wang <>
 kernel/bpf/btf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 138f030..2a85f91 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -2202,6 +2202,9 @@ static struct btf *btf_parse(void __user *btf_data, u32 btf_data_size,
 		goto errout;
+	memcpy(data, &btf->hdr,
+		min_t(u32, btf->hdr.hdr_len, sizeof(btf->hdr)));
 	err = btf_parse_str_sec(env);
 	if (err)
 		goto errout;

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2018-10-24 11:37 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2018-10-19 22:29 [PATCH] bpf: btf: Fix a missing-check bug Wenwen Wang
2018-10-22 15:40 ` Martin Lau
2018-10-22 15:57 ` Y Song
2018-10-24  9:16   ` Daniel Borkmann
2018-10-24 11:36     ` Wenwen Wang

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