bpf: fix divides by zero

[ upstream commit c366287ebd698ef5e3de300d90cd62ee9ee7373e ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index aaa44244d4982491c5fa915a83557b46e559045d..2246115365d99fbd614365e1593e616bc77f66f2 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -949,7 +949,7 @@ 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);
@@ -968,7 +968,7 @@ 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);