Messages in this thread | | | Date | Tue, 08 Aug 2017 10:46:52 +0200 | From | Daniel Borkmann <> | Subject | Re: [RFC PATCH 2/2] bpf: Initialise mod[] in bpf_trace_printk |
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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?
> int fmt_cnt = 0; > u64 unsafe_addr; > char buf[64]; >
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