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bpf: reject out-of-bounds stack pointer calculation

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From: Jann Horn <jannh@google.com>

Reject programs that compute wildly out-of-bounds stack pointers.
Otherwise, pointers can be computed with an offset that doesn't fit into an
`int`, causing security issues in the stack memory access check (as well as
signed integer overflow during offset addition).

This is a fix specifically for the v4.9 stable tree because the mainline
code looks very different at this point.

Fixes: 7bca0a9702 ("bpf: enhance verifier to understand stack pointer arithmetic")
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Borkmann 2017-12-22 16:29:04 +01:00 committed by Greg Kroah-Hartman
parent 7b5b73ea87
commit d75d3ee237
1 changed files with 20 additions and 2 deletions
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22
kernel/bpf/verifier.c
View file

@ -1861,10 +1861,28 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
((BPF_SRC(insn->code) == BPF_X &&
regs[insn->src_reg].type == CONST_IMM) ||
BPF_SRC(insn->code) == BPF_K)) {
if (BPF_SRC(insn->code) == BPF_X)
if (BPF_SRC(insn->code) == BPF_X) {
/* check in case the register contains a big
* 64-bit value
*/
if (regs[insn->src_reg].imm < -MAX_BPF_STACK ||
regs[insn->src_reg].imm > MAX_BPF_STACK) {
verbose("R%d value too big in R%d pointer arithmetic\n",
insn->src_reg, insn->dst_reg);
return -EACCES;
}
dst_reg->imm += regs[insn->src_reg].imm;
else
} else {
/* safe against overflow: addition of 32-bit
* numbers in 64-bit representation
*/
dst_reg->imm += insn->imm;
}
if (dst_reg->imm > 0 || dst_reg->imm < -MAX_BPF_STACK) {
verbose("R%d out-of-bounds pointer arithmetic\n",
insn->dst_reg);
return -EACCES;
}
return 0;
} else if (opcode == BPF_ADD &&
BPF_CLASS(insn->code) == BPF_ALU64 &&