[PATCH v6 04/26] perf trace: Bounds check augmented arguments before reading them

[Ian Rogers <irogers@google.com>]

syscall_arg__scnprintf_buf() and syscall_arg__scnprintf_augmented_string()
trust the augmented arg's size, so a bad one reads out of bounds:

  #3 0x4c0fa0 in syscall_arg__scnprintf_buf builtin-trace.c:1955
  #4 0x4c2f3d in syscall_arg_fmt__scnprintf_val builtin-trace.c:2632
  #5 0x4c33ae in syscall__scnprintf_args builtin-trace.c:2722
  #6 0x4c43d3 in trace__sys_enter builtin-trace.c:3094
  #7 0x4c7865 in trace__handle_event builtin-trace.c:4013

Move the check in btf_struct_scnprintf() to a helper,
syscall_arg__augmented_args_valid(), and use it in both. When the check
fails, syscall_arg__scnprintf_filename() now falls back to vfs_getname or
the pointer.

Reported-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Closes: https://lore.kernel.org/linux-perf-users/arJ-gpzqOHk-gF8T@x2/
Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/builtin-trace.c       | 23 ++++++++++++++---------
 tools/perf/trace/beauty/beauty.h | 17 +++++++++++++++++
 2 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index c39de91140a0..85db74965280 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -1139,14 +1139,11 @@ static size_t btf_struct_scnprintf(const struct btf_type *type, struct btf *btf,
 	LIBBPF_OPTS(btf_dump_opts, dump_opts);
 	LIBBPF_OPTS(btf_dump_type_data_opts, dump_data_opts);
 
-	if (arg == NULL || arg->augmented.args == NULL || arg->augmented.size < (int)sizeof(*augmented_arg) ||
+	if (!syscall_arg__augmented_args_valid(arg, type->size) ||
 	    arg->fmt == NULL || !arg->fmt->from_user)
 		return 0;
 
 	augmented_arg = arg->augmented.args;
-	if (augmented_arg->size <= 0 || augmented_arg->size > arg->augmented.size - (int)sizeof(*augmented_arg) ||
-	    (size_t)augmented_arg->size < type->size)
-		return 0;
 
 	dump_data_opts.compact	  = true;
 	dump_data_opts.skip_names = !arg->trace->show_arg_names;
@@ -1904,12 +1901,18 @@ static void thread__set_filename_pos(struct thread *thread, const char *bf,
 static size_t syscall_arg__scnprintf_augmented_string(struct syscall_arg *arg, char *bf, size_t size)
 {
 	struct augmented_arg *augmented_arg = arg->augmented.args;
-	size_t printed = scnprintf(bf, size, "\"%.*s\"", augmented_arg->size, augmented_arg->value);
+	size_t printed;
+	int consumed;
+
+	if (!syscall_arg__augmented_args_valid(arg, 0))
+		return 0;
+
+	printed = scnprintf(bf, size, "\"%.*s\"", augmented_arg->size, augmented_arg->value);
 	/*
 	 * So that the next arg with a payload can consume its augmented arg, i.e. for rename* syscalls
 	 * we would have two strings, each prefixed by its size.
 	 */
-	int consumed = sizeof(*augmented_arg) + augmented_arg->size;
+	consumed = sizeof(*augmented_arg) + augmented_arg->size;
 
 	arg->augmented.args = ((void *)arg->augmented.args) + consumed;
 	arg->augmented.size -= consumed;
@@ -1922,7 +1925,7 @@ static size_t syscall_arg__scnprintf_filename(char *bf, size_t size,
 {
 	unsigned long ptr = arg->val;
 
-	if (arg->augmented.args)
+	if (syscall_arg__augmented_args_valid(arg, 0))
 		return syscall_arg__scnprintf_augmented_string(arg, bf, size);
 
 	if (!arg->trace->vfs_getname)
@@ -1938,13 +1941,15 @@ static size_t syscall_arg__scnprintf_filename(char *bf, size_t size,
 static size_t syscall_arg__scnprintf_buf(char *bf, size_t size, struct syscall_arg *arg)
 {
 	struct augmented_arg *augmented_arg = arg->augmented.args;
-	unsigned char *orig = (unsigned char *)augmented_arg->value;
 	size_t printed = 0;
+	unsigned char *orig;
 	int consumed;
 
-	if (augmented_arg == NULL)
+	if (!syscall_arg__augmented_args_valid(arg, 0))
 		return 0;
 
+	orig = (unsigned char *)augmented_arg->value;
+
 	for (int j = 0; j < augmented_arg->size; ++j) {
 		bool control_char = orig[j] <= MAX_CONTROL_CHAR || orig[j] >= MAX_ASCII;
 		/* print control characters (0~31 and 127), and non-ascii characters in \(digits) */
diff --git a/tools/perf/trace/beauty/beauty.h b/tools/perf/trace/beauty/beauty.h
index 0f4801c61a5b..1cd307328bb2 100644
--- a/tools/perf/trace/beauty/beauty.h
+++ b/tools/perf/trace/beauty/beauty.h
@@ -124,6 +124,23 @@ struct syscall_arg {
 
 unsigned long syscall_arg__val(struct syscall_arg *arg, u8 idx);
 
+/* Is there a whole augmented arg left with at least @need bytes of payload? */
+static inline bool syscall_arg__augmented_args_valid(struct syscall_arg *arg, size_t need)
+{
+	const struct augmented_arg *augmented_arg;
+
+	if (arg == NULL || arg->augmented.args == NULL ||
+	    arg->augmented.size < (int)sizeof(*augmented_arg))
+		return false;
+
+	augmented_arg = arg->augmented.args;
+	if (augmented_arg->size < 0 ||
+	    augmented_arg->size > arg->augmented.size - (int)sizeof(*augmented_arg))
+		return false;
+
+	return (size_t)augmented_arg->size >= need;
+}
+
 size_t syscall_arg__scnprintf_strarray_flags(char *bf, size_t size, struct syscall_arg *arg);
 #define SCA_STRARRAY_FLAGS syscall_arg__scnprintf_strarray_flags
 
-- 
2.56.0.rc1.315.gc6ed9934b7-goog