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

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: net...@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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