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Commit 68fda450 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Daniel Borkmann
Browse files

bpf: fix 32-bit divide by zero 



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: 62258278 ("net: filter: x86: internal BPF JIT")
Fixes: 7a12b503 ("sparc64: Add eBPF JIT.")
Reported-by: default avatar <syzbot+48340bb518e88849e2e3@syzkaller.appspotmail.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent c366287e

kernel/bpf/verifier.c

+18 −0
Original line number Diff line number Diff line
@@ -4445,6 +4445,24 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) 
	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;

net/core/filter.c

+4 −0
Original line number Diff line number Diff line
@@ -458,6 +458,10 @@ static int bpf_convert_filter(struct sock_filter *prog, int len, 
			    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;