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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 9d7eceede7
("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>
This commit is contained in:
Daniel Borkmann 2021-03-23 08:51:02 +01:00
parent 6f55b2f2a1
commit 24c109bb15
1 changed files with 9 additions and 10 deletions
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19
kernel/bpf/verifier.c
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@ -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;
}