[PATCH v3 04/13] tracing/probes: Fix missing BTF kind checks in char pointer/array helpers

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

In struct btf_type, the type ID and byte size share a union, and only
BTF_KIND_INT types are followed by a 32-bit integer encoding word.
Because btf_type_is_char_ptr() and btf_type_is_char_array() do not
verify that the outer type is BTF_KIND_PTR or that the resolved element
type is a non-NULL BTF_KIND_INT before inspecting it, non-pointer BTF
types can have their byte size misinterpreted as a BTF type ID, and
arrays of non-integer types read out-of-bounds or misinterpret trailing
BTF metadata as BTF_INT_* encoding bits.

Validate the BTF type kinds and NULL pointers before reading inner type
metadata in both helpers.

Fixes: 27973e5c64b9 ("tracing/probes: Add string type check with BTF")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/trace_probe.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 54cd3c2584a8..b8f6a36ee0d4 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -411,6 +411,9 @@ static bool btf_type_is_char_ptr(struct btf *btf, const struct btf_type *type)
 	const struct btf_type *real_type;
 	u32 intdata;
 
+	if (BTF_INFO_KIND(type->info) != BTF_KIND_PTR)
+		return false;
+
 	real_type = btf_type_skip_modifiers(btf, type->type, NULL);
 	if (!real_type)
 		return false;
@@ -435,6 +438,11 @@ static bool btf_type_is_char_array(struct btf *btf, const struct btf_type *type)
 	array = (const struct btf_array *)(type + 1);
 
 	real_type = btf_type_skip_modifiers(btf, array->type, NULL);
+	if (!real_type)
+		return false;
+
+	if (BTF_INFO_KIND(real_type->info) != BTF_KIND_INT)
+		return false;
 
 	intdata = btf_type_int(real_type);
 	return !(BTF_INT_ENCODING(intdata) & BTF_INT_SIGNED)