This is a note to let you know that I've just added the patch titled bpf: Ensure off_reg has no mixed signed bounds for all types to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bpf-ensure-off_reg-has-no-mixed-signed-bounds-for-al.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit f00b2aca742f924e0b814d6f35226161ba578446 Author: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Date: Tue Mar 23 08:51:02 2021 +0100 bpf: Ensure off_reg has no mixed signed bounds for all types [ Upstream commit 24c109bb1537c12c02aeed2d51a347b4d6a9b76e ] The mixed signed bounds check really belongs into retrieve_ptr_limit() instead of outside of it in adjust_ptr_min_max_vals(). The reason is that this check is not tied to PTR_TO_MAP_VALUE only, but to all pointer types that we handle in retrieve_ptr_limit() and given errors from the latter propagate back to adjust_ptr_min_max_vals() and lead to rejection of the program, it's a better place to reside to avoid anything slipping through for future types. The reason why we must reject such off_reg is that we otherwise would not be able to derive a mask, see details in 9d7eceede769 ("bpf: restrict unknown scalars of mixed signed bounds for unprivileged"). Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Reviewed-by: John Fastabend <john.fastabend@xxxxxxxxx> Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 2eaefd9c4152..a2a74b7ed2c6 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5329,12 +5329,18 @@ static struct bpf_insn_aux_data *cur_aux(struct bpf_verifier_env *env) } static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, - u32 *ptr_limit, u8 opcode, bool off_is_neg) + const struct bpf_reg_state *off_reg, + u32 *ptr_limit, u8 opcode) { + bool off_is_neg = off_reg->smin_value < 0; bool mask_to_left = (opcode == BPF_ADD && off_is_neg) || (opcode == BPF_SUB && !off_is_neg); u32 off, max; + if (!tnum_is_const(off_reg->var_off) && + (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) + return -EACCES; + switch (ptr_reg->type) { case PTR_TO_STACK: /* Offset 0 is out-of-bounds, but acceptable start for the @@ -5427,7 +5433,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, alu_state |= ptr_is_dst_reg ? BPF_ALU_SANITIZE_SRC : BPF_ALU_SANITIZE_DST; - err = retrieve_ptr_limit(ptr_reg, &alu_limit, opcode, off_is_neg); + err = retrieve_ptr_limit(ptr_reg, off_reg, &alu_limit, opcode); if (err < 0) return err; @@ -5472,8 +5478,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, smin_ptr = ptr_reg->smin_value, smax_ptr = ptr_reg->smax_value; u64 umin_val = off_reg->umin_value, umax_val = off_reg->umax_value, umin_ptr = ptr_reg->umin_value, umax_ptr = ptr_reg->umax_value; - u32 dst = insn->dst_reg, src = insn->src_reg; u8 opcode = BPF_OP(insn->code); + u32 dst = insn->dst_reg; int ret; dst_reg = ®s[dst]; @@ -5521,13 +5527,6 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, verbose(env, "R%d pointer arithmetic on %s prohibited\n", dst, reg_type_str[ptr_reg->type]); return -EACCES; - case PTR_TO_MAP_VALUE: - if (!env->env->bypass_spec_v1 && !known && (smin_val < 0) != (smax_val < 0)) { - verbose(env, "R%d has unknown scalar with mixed signed bounds, pointer arithmetic with it prohibited for !root\n", - off_reg == dst_reg ? dst : src); - return -EACCES; - } - fallthrough; default: break; }