Messages in this thread | | | Subject | Re: [RFC] [PATCH bpf-next 1/1] bpf: Clear the noisy tail buffer for bpf_d_path() helper | From | xufeng zhang <> | Date | Wed, 24 Nov 2021 12:15:34 +0800 |
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Jiri and KP,
Any suggestion?
Thanks in advance!
Xufeng
在 2021/11/20 下午1:18, Xufeng Zhang 写道: > From: "Xufeng Zhang" <yunbo.xufeng@linux.alibaba.com> > > The motivation behind this change is to use the returned full path > for lookup keys in BPF_MAP_TYPE_HASH map. > bpf_d_path() prepend the path string from the end of the input > buffer, and call memmove() to copy the full path from the tail > buffer to the head of buffer before return. So although the > returned buffer string is NULL terminated, there is still > noise data at the tail of buffer. > If using the returned full path buffer as the key of hash map, > the noise data is also calculated and makes map lookup failed. > To resolve this problem, we could memset the noisy tail buffer > before return. > > Signed-off-by: Xufeng Zhang <yunbo.xufeng@linux.alibaba.com> > --- > kernel/trace/bpf_trace.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 25ea521fb8f1..ec4a6823c024 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -903,6 +903,8 @@ BPF_CALL_3(bpf_d_path, struct path *, path, char *, buf, u32, sz) > } else { > len = buf + sz - p; > memmove(buf, p, len); > + /* Clear the noisy tail buffer before return */ > + memset(buf + len, 0, sz - len); > } > > return len;
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