perf bpf-utils: Harden get_bpf_prog_info_linear

In get_bpf_prog_info_linear two calls to bpf_obj_get_info_by_fd are
made, the first to compute memory requirements for a struct perf_bpil
and the second to fill it in. Previously the code would warn when the
second call didn't match the first. Such races can be common place in
things like perf test, whose perf trace tests will frequently load BPF
programs. Rather than a debug message, return actual errors for this
case. Out of paranoia also validate the read bpf_prog_info array
value. Change the type of ptr to avoid mismatched pointer type
compiler warnings. Add some additional debug print outs and sanity
asserts.

Closes: https://lore.kernel.org/lkml/CAP-5=[e-mail]/
Fixes: 6ac22d036f86 ("perf bpf: Pull in bpf_program__get_prog_info_linear()")
Reviewed-by: Namhyung Kim <[e-mail]>
Signed-off-by: Ian Rogers <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/util/bpf-utils.c

···
 	__u32 info_len = sizeof(info);
 	__u32 data_len = 0;
 	int i, err;
-	void *ptr;
+	__u8 *ptr;
 
 	if (arrays >> PERF_BPIL_LAST_ARRAY)
 		return ERR_PTR(-EINVAL);
···
 		pr_debug("can't get prog info: %s", strerror(errno));
 		return ERR_PTR(-EFAULT);
 	}
+	if (info.type >= __MAX_BPF_PROG_TYPE)
+		pr_debug("%s:%d: unexpected program type %u\n", __func__, __LINE__, info.type);
 
 	/* step 2: calculate total size of all arrays */
 	for (i = PERF_BPIL_FIRST_ARRAY; i < PERF_BPIL_LAST_ARRAY; ++i) {
···
 					     desc->count_offset, count);
 		bpf_prog_info_set_offset_u32(&info_linear->info,
 					     desc->size_offset, size);
+		assert(ptr >= info_linear->data);
+		assert(ptr < &info_linear->data[data_len]);
 		bpf_prog_info_set_offset_u64(&info_linear->info,
 					     desc->array_offset,
 					     ptr_to_u64(ptr));
···
 		free(info_linear);
 		return ERR_PTR(-EFAULT);
 	}
+	if (info_linear->info.type >= __MAX_BPF_PROG_TYPE) {
+		pr_debug("%s:%d: unexpected program type %u\n",
+			 __func__, __LINE__, info_linear->info.type);
+	}
 
 	/* step 6: verify the data */
+	ptr = info_linear->data;
 	for (i = PERF_BPIL_FIRST_ARRAY; i < PERF_BPIL_LAST_ARRAY; ++i) {
 		const struct bpil_array_desc *desc = &bpil_array_desc[i];
-		__u32 v1, v2;
+		__u32 count1, count2, size1, size2;
+		__u64 ptr2;
 
 		if ((arrays & (1UL << i)) == 0)
 			continue;
 
-		v1 = bpf_prog_info_read_offset_u32(&info, desc->count_offset);
-		v2 = bpf_prog_info_read_offset_u32(&info_linear->info,
+		count1 = bpf_prog_info_read_offset_u32(&info, desc->count_offset);
+		count2 = bpf_prog_info_read_offset_u32(&info_linear->info,
 						   desc->count_offset);
-		if (v1 != v2)
-			pr_warning("%s: mismatch in element count\n", __func__);
+		if (count1 != count2) {
+			pr_warning("%s: mismatch in element count %u vs %u\n", __func__, count1, count2);
+			free(info_linear);
+			return ERR_PTR(-ERANGE);
+		}
 
-		v1 = bpf_prog_info_read_offset_u32(&info, desc->size_offset);
-		v2 = bpf_prog_info_read_offset_u32(&info_linear->info,
+		size1 = bpf_prog_info_read_offset_u32(&info, desc->size_offset);
+		size2 = bpf_prog_info_read_offset_u32(&info_linear->info,
 						   desc->size_offset);
-		if (v1 != v2)
-			pr_warning("%s: mismatch in rec size\n", __func__);
+		if (size1 != size2) {
+			pr_warning("%s: mismatch in rec size %u vs %u\n", __func__, size1, size2);
+			free(info_linear);
+			return ERR_PTR(-ERANGE);
+		}
+		ptr2 = bpf_prog_info_read_offset_u64(&info_linear->info, desc->array_offset);
+		if (ptr_to_u64(ptr) != ptr2) {
+			pr_warning("%s: mismatch in array %p vs %llx\n", __func__, ptr, ptr2);
+			free(info_linear);
+			return ERR_PTR(-ERANGE);
+		}
+		ptr += roundup(count1 * size1, sizeof(__u64));
 	}
 
 	/* step 7: update info_len and data_len */