Messages in this thread | | | Date | Tue, 08 Aug 2017 09:48:57 -0700 (PDT) | Subject | Re: [RFC PATCH 2/2] bpf: Initialise mod[] in bpf_trace_printk | From | David Miller <> |
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From: Daniel Borkmann <daniel@iogearbox.net> Date: Tue, 08 Aug 2017 10:46:52 +0200
> On 08/08/2017 12:25 AM, James Hogan wrote: >> In bpf_trace_printk(), the elements in mod[] are left uninitialised, >> but >> they are then incremented to track the width of the formats. Zero >> initialise the array just in case the memory contains non-zero values >> on >> entry. >> >> Fixes: 9c959c863f82 ("tracing: Allow BPF programs to call >> bpf_trace_printk()") >> Signed-off-by: James Hogan <james.hogan@imgtec.com> >> Cc: Alexei Starovoitov <ast@kernel.org> >> Cc: Daniel Borkmann <daniel@iogearbox.net> >> Cc: Steven Rostedt <rostedt@goodmis.org> >> Cc: Ingo Molnar <mingo@redhat.com> >> Cc: netdev@vger.kernel.org >> --- >> When I checked (on MIPS32), the elements tended to have the value zero >> anyway (does BPF zero the stack or something clever?), so this is a >> purely theoretical fix. >> --- >> kernel/trace/bpf_trace.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c >> index 32dcbe1b48f2..86a52857d941 100644 >> --- a/kernel/trace/bpf_trace.c >> +++ b/kernel/trace/bpf_trace.c >> @@ -129,7 +129,7 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, >> fmt_size, u64, arg1, >> u64, arg2, u64, arg3) >> { >> bool str_seen = false; >> - int mod[3] = {}; >> + int mod[3] = { 0, 0, 0 }; > > I'm probably missing something, but is the behavior of gcc wrt > above initializers different on mips (it zeroes just fine on x86 > at least)? If yes, we'd probably need a cocci script to also check > rest of the kernel given this is used in a number of places. Hm, > could you elaborate?
This change is not necessary at all.
An empty initializer must clear the whole object to zero.
"theoretical" fix indeed... :-(
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