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arm64: bpf: fix out-of-bounds read in bpf2a64_offset()
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Problems occur when bpf_to or bpf_from has value prog->len - 1 (e.g.,
"Very long jump backwards" in test_bpf where the last instruction is a
jump): since ctx->offset has length prog->len, ctx->offset[bpf_to + 1]
or ctx->offset[bpf_from + 1] will cause an out-of-bounds read, leading
to a bogus jump offset and kernel panic.

This patch moves updating ctx->offset to after calling build_insn(),
and changes indexing to use bpf_to and bpf_from without + 1.

Fixes: e54bcde ("arm64: eBPF JIT compiler")
Cc: <stable@vger.kernel.org> # 3.18+
Cc: Zi Shen Lim <zlim.lnx@gmail.com>
Cc: Will Deacon <will.deacon@arm.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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xiw authored and ctmarinas committed Jun 25, 2015
1 parent be081d9 commit 8eee539
Showing 1 changed file with 4 additions and 3 deletions.
7 changes: 4 additions & 3 deletions arch/arm64/net/bpf_jit_comp.c
Original file line number Diff line number Diff line change
Expand Up @@ -113,9 +113,9 @@ static inline void emit_a64_mov_i(const int is64, const int reg,
static inline int bpf2a64_offset(int bpf_to, int bpf_from,
const struct jit_ctx *ctx)
{
int to = ctx->offset[bpf_to + 1];
int to = ctx->offset[bpf_to];
/* -1 to account for the Branch instruction */
int from = ctx->offset[bpf_from + 1] - 1;
int from = ctx->offset[bpf_from] - 1;

return to - from;
}
Expand Down Expand Up @@ -640,10 +640,11 @@ static int build_body(struct jit_ctx *ctx)
const struct bpf_insn *insn = &prog->insnsi[i];
int ret;

ret = build_insn(insn, ctx);

if (ctx->image == NULL)
ctx->offset[i] = ctx->idx;

ret = build_insn(insn, ctx);
if (ret > 0) {
i++;
continue;
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