[PATCH bpf-next v3 0/2] bpf: fix null pointer access for malformed BPF_CORE_TYPE_ID_LOCAL relos

[PATCH bpf-next v3 0/2] bpf: fix null pointer access for malformed BPF_CORE_TYPE_ID_LOCAL relos

[Eduard Zingerman]

Liu RuiTong reported an in-kernel null pointer derefence when
processing BPF_CORE_TYPE_ID_LOCAL relocations referencing non-existing
BTF types. Fix this by adding proper id checks.

Changes v2->v3:
- selftest update suggested by Andrii:
  avoid memset(0) for log buffer and do memset(0) for bpf_attr.

Changes v1->v2:
- moved check from bpf_core_calc_relo_insn() to bpf_core_apply()
  now both in kernel and in libbpf relocation type id is guaranteed
  to exist when bpf_core_calc_relo_insn() is called;
- added a test case.

v1: https://lore.kernel.org/bpf/20240821164620.1056362-1-eddyz87@gmail.com/
v2: https://lore.kernel.org/bpf/20240822001837.2715909-1-eddyz87@gmail.com/

Eduard Zingerman (2):
  bpf: correctly handle malformed BPF_CORE_TYPE_ID_LOCAL relos
  selftests/bpf: test for malformed BPF_CORE_TYPE_ID_LOCAL relocation

 kernel/bpf/btf.c                              |   8 ++
 .../selftests/bpf/prog_tests/core_reloc_raw.c | 125 ++++++++++++++++++
 2 files changed, 133 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c

-- 
2.45.2

[PATCH bpf-next v3 1/2] bpf: correctly handle malformed BPF_CORE_TYPE_ID_LOCAL relos

[Eduard Zingerman]

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: 74753e1462e7 ("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>
---
 kernel/bpf/btf.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index c9338fb397fc..5de424d3a795 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -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_relo_res targ_res;
 	struct bpf_core_spec *specs;
+	const struct btf_type *type;
 	int err;
 
 	/* ~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)
 		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) {
 		struct bpf_cand_cache *cc;
 		int i;
-- 
2.45.2

[PATCH bpf-next v3 2/2] selftests/bpf: test for malformed BPF_CORE_TYPE_ID_LOCAL relocation

[Eduard Zingerman]

Check that verifier rejects BPF program containing relocation
pointing to non-existent BTF type.

To force relocation resolution on kernel side test case uses
bpf_attr->core_relos field. This field is not exposed by libbpf,
so directly do BPF system call in the test.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 .../selftests/bpf/prog_tests/core_reloc_raw.c | 125 ++++++++++++++++++
 1 file changed, 125 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c

diff --git a/tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c b/tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c
new file mode 100644
index 000000000000..a18d3680fb16
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/* Test cases that can't load programs using libbpf and need direct
+ * BPF syscall access
+ */
+
+#include <sys/syscall.h>
+#include <bpf/libbpf.h>
+#include <bpf/btf.h>
+
+#include "test_progs.h"
+#include "test_btf.h"
+#include "bpf/libbpf_internal.h"
+
+static char log[16 * 1024];
+
+/* Check that verifier rejects BPF program containing relocation
+ * pointing to non-existent BTF type.
+ */
+static void test_bad_local_id(void)
+{
+	struct test_btf {
+		struct btf_header hdr;
+		__u32 types[15];
+		char strings[128];
+	} raw_btf = {
+		.hdr = {
+			.magic = BTF_MAGIC,
+			.version = BTF_VERSION,
+			.hdr_len = sizeof(struct btf_header),
+			.type_off = 0,
+			.type_len = sizeof(raw_btf.types),
+			.str_off = offsetof(struct test_btf, strings) -
+				   offsetof(struct test_btf, types),
+			.str_len = sizeof(raw_btf.strings),
+		},
+		.types = {
+			BTF_PTR_ENC(0),					/* [1] void*  */
+			BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4),	/* [2] int    */
+			BTF_FUNC_PROTO_ENC(2, 1),			/* [3] int (*)(void*) */
+			BTF_FUNC_PROTO_ARG_ENC(8, 1),
+			BTF_FUNC_ENC(8, 3)			/* [4] FUNC 'foo' type_id=2   */
+		},
+		.strings = "\0int\0 0\0foo\0"
+	};
+	__u32 log_level = 1 | 2 | 4;
+	LIBBPF_OPTS(bpf_btf_load_opts, opts,
+		    .log_buf = log,
+		    .log_size = sizeof(log),
+		    .log_level = log_level,
+	);
+	struct bpf_insn insns[] = {
+		BPF_ALU64_IMM(BPF_MOV, BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	struct bpf_func_info funcs[] = {
+		{
+			.insn_off = 0,
+			.type_id = 4,
+		}
+	};
+	struct bpf_core_relo relos[] = {
+		{
+			.insn_off = 0,		/* patch first instruction (r0 = 0) */
+			.type_id = 100500,	/* !!! this type id does not exist */
+			.access_str_off = 6,	/* offset of "0" */
+			.kind = BPF_CORE_TYPE_ID_LOCAL,
+		}
+	};
+	union bpf_attr attr;
+	int saved_errno;
+	int prog_fd = -1;
+	int btf_fd = -1;
+
+	btf_fd = bpf_btf_load(&raw_btf, sizeof(raw_btf), &opts);
+	saved_errno = errno;
+	if (btf_fd < 0 || env.verbosity > VERBOSE_NORMAL) {
+		printf("-------- BTF load log start --------\n");
+		printf("%s", log);
+		printf("-------- BTF load log end ----------\n");
+	}
+	if (btf_fd < 0) {
+		PRINT_FAIL("bpf_btf_load() failed, errno=%d\n", saved_errno);
+		return;
+	}
+
+	log[0] = 0;
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_btf_fd = btf_fd;
+	attr.prog_type = BPF_TRACE_RAW_TP;
+	attr.license = (__u64)"GPL";
+	attr.insns = (__u64)&insns;
+	attr.insn_cnt = sizeof(insns) / sizeof(*insns);
+	attr.log_buf = (__u64)log;
+	attr.log_size = sizeof(log);
+	attr.log_level = log_level;
+	attr.func_info = (__u64)funcs;
+	attr.func_info_cnt = sizeof(funcs) / sizeof(*funcs);
+	attr.func_info_rec_size = sizeof(*funcs);
+	attr.core_relos = (__u64)relos;
+	attr.core_relo_cnt = sizeof(relos) / sizeof(*relos);
+	attr.core_relo_rec_size = sizeof(*relos);
+	prog_fd = sys_bpf_prog_load(&attr, sizeof(attr), 1);
+	saved_errno = errno;
+	if (prog_fd < 0 || env.verbosity > VERBOSE_NORMAL) {
+		printf("-------- program load log start --------\n");
+		printf("%s", log);
+		printf("-------- program load log end ----------\n");
+	}
+	if (prog_fd >= 0) {
+		PRINT_FAIL("sys_bpf_prog_load() expected to fail\n");
+		goto out;
+	}
+	ASSERT_HAS_SUBSTR(log, "relo #0: bad type id 100500", "program load log");
+
+out:
+	close(prog_fd);
+	close(btf_fd);
+}
+
+void test_core_reloc_raw(void)
+{
+	if (test__start_subtest("bad_local_id"))
+		test_bad_local_id();
+}
-- 
2.45.2

Re: [PATCH bpf-next v3 0/2] bpf: fix null pointer access for malformed BPF_CORE_TYPE_ID_LOCAL relos

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Thu, 22 Aug 2024 01:01:22 -0700 you wrote:
> Liu RuiTong reported an in-kernel null pointer derefence when
> processing BPF_CORE_TYPE_ID_LOCAL relocations referencing non-existing
> BTF types. Fix this by adding proper id checks.
> 
> Changes v2->v3:
> - selftest update suggested by Andrii:
>   avoid memset(0) for log buffer and do memset(0) for bpf_attr.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v3,1/2] bpf: correctly handle malformed BPF_CORE_TYPE_ID_LOCAL relos
    https://git.kernel.org/bpf/bpf-next/c/3d2786d65aaa
  - [bpf-next,v3,2/2] selftests/bpf: test for malformed BPF_CORE_TYPE_ID_LOCAL relocation
    https://git.kernel.org/bpf/bpf-next/c/110bbd3a2ed7

You are awesome, thank you!
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