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bpf: correctly handle malformed BPF_CORE_TYPE_ID_LOCAL relos

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In case of malformed relocation record of kind BPF_CORE_TYPE_ID_LOCAL
referencing a non-existing BTF type, function bpf_core_calc_relo_insn
would cause a null pointer deference.

Fix this by adding a proper check upper in call stack, as malformed
relocation records could be passed from user space.

Simplest reproducer is a program:

    r0 = 0
    exit

With a single relocation record:

    .insn_off = 0,          /* patch first instruction */
    .type_id = 100500,      /* this type id does not exist */
    .access_str_off = 6,    /* offset of string "0" */
    .kind = BPF_CORE_TYPE_ID_LOCAL,

See the link for original reproducer or next commit for a test case.

Fixes: 74753e1462 ("libbpf: Replace btf__type_by_id() with btf_type_by_id().")
Reported-by: Liu RuiTong <cnitlrt@gmail.com>
Closes: https://lore.kernel.org/bpf/CAK55_s6do7C+DVwbwY_7nKfUz0YLDoiA1v6X3Y9+p0sWzipFSA@mail.gmail.com/
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240822080124.2995724-2-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Eduard Zingerman 2024-08-22 01:01:23 -07:00 committed by Alexei Starovoitov
parent b6ab509027
commit 3d2786d65a
1 changed files with 8 additions and 0 deletions
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8
kernel/bpf/btf.c
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@ -8910,6 +8910,7 @@ int bpf_core_apply(struct bpf_core_ctx *ctx, const struct bpf_core_relo *relo,
struct bpf_core_cand_list cands = {}; struct bpf_core_cand_list cands = {};
struct bpf_core_relo_res targ_res; struct bpf_core_relo_res targ_res;
struct bpf_core_spec *specs; struct bpf_core_spec *specs;
const struct btf_type *type;
int err; int err;
/* ~4k of temp memory necessary to convert LLVM spec like "0:1:0:5" /* ~4k of temp memory necessary to convert LLVM spec like "0:1:0:5"
@ -8919,6 +8920,13 @@ int bpf_core_apply(struct bpf_core_ctx *ctx, const struct bpf_core_relo *relo,
if (!specs) if (!specs)
return -ENOMEM; return -ENOMEM;
type = btf_type_by_id(ctx->btf, relo->type_id);
if (!type) {
bpf_log(ctx->log, "relo #%u: bad type id %u\n",
relo_idx, relo->type_id);
return -EINVAL;
}
if (need_cands) { if (need_cands) {
struct bpf_cand_cache *cc; struct bpf_cand_cache *cc;
int i; int i;