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authorDaniel Borkmann <daniel@iogearbox.net>2017-10-21 02:34:21 +0200
committerDavid S. Miller <davem@davemloft.net>2017-10-22 00:56:09 +0100
commitfb2a311a31d3457fe8c3ee16f5609877e2ead9f7 (patch)
tree07c6622bd68796f908b44e1f0af8742682f04b49
parent8695a5395661fbb4a4f26c97f801f3800ae4754e (diff)
downloadlinux-sh-fb2a311a31d3457fe8c3ee16f5609877e2ead9f7.tar.gz
bpf: fix off by one for range markings with L{T, E} patterns
During review I noticed that the current logic for direct packet access marking in check_cond_jmp_op() has an off by one for the upper right range border when marking in find_good_pkt_pointers() with BPF_JLT and BPF_JLE. It's not really harmful given access up to pkt_end is always safe, but we should nevertheless correct the range marking before it becomes ABI. If pkt_data' denotes a pkt_data derived pointer (pkt_data + X), then for pkt_data' < pkt_end in the true branch as well as for pkt_end <= pkt_data' in the false branch we mark the range with X although it should really be X - 1 in these cases. For example, X could be pkt_end - pkt_data, then when testing for pkt_data' < pkt_end the verifier simulation cannot deduce that a byte load of pkt_data' - 1 would succeed in this branch. Fixes: b4e432f1000a ("bpf: enable BPF_J{LT, LE, SLT, SLE} opcodes in verifier") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Acked-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--kernel/bpf/verifier.c33
1 files changed, 21 insertions, 12 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 20f3889c006e..49cb5ad14746 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2430,12 +2430,15 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
}
static void find_good_pkt_pointers(struct bpf_verifier_state *state,
- struct bpf_reg_state *dst_reg)
+ struct bpf_reg_state *dst_reg,
+ bool range_right_open)
{
struct bpf_reg_state *regs = state->regs, *reg;
+ u16 new_range;
int i;
- if (dst_reg->off < 0)
+ if (dst_reg->off < 0 ||
+ (dst_reg->off == 0 && range_right_open))
/* This doesn't give us any range */
return;
@@ -2446,9 +2449,13 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *state,
*/
return;
- /* LLVM can generate four kind of checks:
+ new_range = dst_reg->off;
+ if (range_right_open)
+ new_range--;
+
+ /* Examples for register markings:
*
- * Type 1/2:
+ * pkt_data in dst register:
*
* r2 = r3;
* r2 += 8;
@@ -2465,7 +2472,7 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *state,
* r2=pkt(id=n,off=8,r=0)
* r3=pkt(id=n,off=0,r=0)
*
- * Type 3/4:
+ * pkt_data in src register:
*
* r2 = r3;
* r2 += 8;
@@ -2483,7 +2490,9 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *state,
* r3=pkt(id=n,off=0,r=0)
*
* Find register r3 and mark its range as r3=pkt(id=n,off=0,r=8)
- * so that range of bytes [r3, r3 + 8) is safe to access.
+ * or r3=pkt(id=n,off=0,r=8-1), so that range of bytes [r3, r3 + 8)
+ * and [r3, r3 + 8-1) respectively is safe to access depending on
+ * the check.
*/
/* If our ids match, then we must have the same max_value. And we
@@ -2494,14 +2503,14 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *state,
for (i = 0; i < MAX_BPF_REG; i++)
if (regs[i].type == PTR_TO_PACKET && regs[i].id == dst_reg->id)
/* keep the maximum range already checked */
- regs[i].range = max_t(u16, regs[i].range, dst_reg->off);
+ regs[i].range = max(regs[i].range, new_range);
for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) {
if (state->stack_slot_type[i] != STACK_SPILL)
continue;
reg = &state->spilled_regs[i / BPF_REG_SIZE];
if (reg->type == PTR_TO_PACKET && reg->id == dst_reg->id)
- reg->range = max_t(u16, reg->range, dst_reg->off);
+ reg->range = max(reg->range, new_range);
}
}
@@ -2865,19 +2874,19 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JGT &&
dst_reg->type == PTR_TO_PACKET &&
regs[insn->src_reg].type == PTR_TO_PACKET_END) {
- find_good_pkt_pointers(this_branch, dst_reg);
+ find_good_pkt_pointers(this_branch, dst_reg, false);
} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JLT &&
dst_reg->type == PTR_TO_PACKET &&
regs[insn->src_reg].type == PTR_TO_PACKET_END) {
- find_good_pkt_pointers(other_branch, dst_reg);
+ find_good_pkt_pointers(other_branch, dst_reg, true);
} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JGE &&
dst_reg->type == PTR_TO_PACKET_END &&
regs[insn->src_reg].type == PTR_TO_PACKET) {
- find_good_pkt_pointers(other_branch, &regs[insn->src_reg]);
+ find_good_pkt_pointers(other_branch, &regs[insn->src_reg], false);
} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JLE &&
dst_reg->type == PTR_TO_PACKET_END &&
regs[insn->src_reg].type == PTR_TO_PACKET) {
- find_good_pkt_pointers(this_branch, &regs[insn->src_reg]);
+ find_good_pkt_pointers(this_branch, &regs[insn->src_reg], true);
} else if (is_pointer_value(env, insn->dst_reg)) {
verbose("R%d pointer comparison prohibited\n", insn->dst_reg);
return -EACCES;