From: Daniel Borkmann <dan...@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.ho...@imgtec.com>
>> Cc: Alexei Starovoitov <a...@kernel.org>
>> Cc: Daniel Borkmann <dan...@iogearbox.net>
>> Cc: Steven Rostedt <rost...@goodmis.org>
>> Cc: Ingo Molnar <mi...@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... :-(
