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authorDaniel Borkmann <daniel@iogearbox.net>2021-03-23 08:51:02 +0100
committerDaniel Borkmann <daniel@iogearbox.net>2021-04-16 23:51:39 +0200
commit24c109bb1537c12c02aeed2d51a347b4d6a9b76e (patch)
tree17362854c4e4a2205a112ffbe9e7c4452a8174ed /kernel
parent6f55b2f2a1178856c19bbce2f71449926e731914 (diff)
bpf: Ensure off_reg has no mixed signed bounds for all types
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@iogearbox.net> Reviewed-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/verifier.c19
1 files changed, 9 insertions, 10 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4ee014dadac7..a21d7f1a0ba8 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5857,12 +5857,18 @@ 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
@@ -5956,7 +5962,7 @@ 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;
@@ -6036,8 +6042,8 @@ 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 = &regs[dst];
@@ -6085,13 +6091,6 @@ 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;
}