[PATCH 4.14 68/71] bpf: fix 32-bit divide by zero

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexei Starovoitov <a...@kernel.org>

[ upstream commit 68fda450a7df51cff9e5a4d4a4d9d0d5f2589153 ]

due to some JITs doing if (src_reg == 0) check in 64-bit mode
for div/mod operations mask upper 32-bits of src register
before doing the check

Fixes: 622582786c9e ("net: filter: x86: internal BPF JIT")
Fixes: 7a12b5031c6b ("sparc64: Add eBPF JIT.")
Reported-by: syzbot+48340bb518e88849e...@syzkaller.appspotmail.com
Signed-off-by: Alexei Starovoitov <a...@kernel.org>
Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 kernel/bpf/verifier.c |   18 ++++++++++++++++++
 net/core/filter.c     |    4 ++++
 2 files changed, 22 insertions(+)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4304,6 +4304,24 @@ static int fixup_bpf_calls(struct bpf_ve
        int i, cnt, delta = 0;
 
        for (i = 0; i < insn_cnt; i++, insn++) {
+               if (insn->code == (BPF_ALU | BPF_MOD | BPF_X) ||
+                   insn->code == (BPF_ALU | BPF_DIV | BPF_X)) {
+                       /* due to JIT bugs clear upper 32-bits of src register
+                        * before div/mod operation
+                        */
+                       insn_buf[0] = BPF_MOV32_REG(insn->src_reg, 
insn->src_reg);
+                       insn_buf[1] = *insn;
+                       cnt = 2;
+                       new_prog = bpf_patch_insn_data(env, i + delta, 
insn_buf, cnt);
+                       if (!new_prog)
+                               return -ENOMEM;
+
+                       delta    += cnt - 1;
+                       env->prog = prog = new_prog;
+                       insn      = new_prog->insnsi + i + delta;
+                       continue;
+               }
+
                if (insn->code != (BPF_JMP | BPF_CALL))
                        continue;
 
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -457,6 +457,10 @@ do_pass:
                            convert_bpf_extensions(fp, &insn))
                                break;
 
+                       if (fp->code == (BPF_ALU | BPF_DIV | BPF_X) ||
+                           fp->code == (BPF_ALU | BPF_MOD | BPF_X))
+                               *insn++ = BPF_MOV32_REG(BPF_REG_X, BPF_REG_X);
+
                        *insn = BPF_RAW_INSN(fp->code, BPF_REG_A, BPF_REG_X, 0, 
fp->k);
                        break;