bpf: fix divides by zero

Divides by zero are not nice, lets avoid them if possible.

Also do_div() seems not needed when dealing with 32bit operands,
but this seems a minor detail.

Fixes: bd4cf0ed331a ("net: filter: rework/optimize internal BPF interpreter's instruction set")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 51ec2dda7f08c6c90af084589bb6d80662c77d12..7949e8b8f94e9cc196e0449214493ccce61b0903 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -956,7 +956,7 @@ select_insn:
                DST = tmp;
                CONT;
        ALU_MOD_X:
-               if (unlikely(SRC == 0))
+               if (unlikely((u32)SRC == 0))
                        return 0;
                tmp = (u32) DST;
                DST = do_div(tmp, (u32) SRC);
@@ -975,7 +975,7 @@ select_insn:
                DST = div64_u64(DST, SRC);
                CONT;
        ALU_DIV_X:
-               if (unlikely(SRC == 0))
+               if (unlikely((u32)SRC == 0))
                        return 0;
                tmp = (u32) DST;
                do_div(tmp, (u32) SRC);