[PATCH perf-tools-next v6 1/5] perf trace: Fix error checking in btf_struct_scnprintf()

[Aaron Tomlin]

btf_dump__dump_type_data() returns the positive number of bytes dumped on
success, or a negative error code (e.g., -EINVAL) on failure.

Currently, btf_struct_scnprintf() checks if btf_dump__dump_type_data()
returns 0. When a negative error code is returned on failure, this check
evaluates to false, causing the function to proceed down the success path
and advance arg->augmented.args past the unprinted struct data before
returning 0.

Consequently, when syscall__scnprintf_args() falls back to the default
argument beautifier upon receiving 0 from trace__btf_scnprintf(), the
fallback beautifier or subsequent arguments read from an erroneously
advanced augmented arguments buffer.

Fix this by checking for '<= 0' ensuring that on any failure or 0-byte
dump, 0 is returned without modifying the augmented arguments pointer.

Fixes: cb32035214b9 ("perf trace: Pretty print augmented struct args using BTF")
Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxxx>
---
 tools/perf/builtin-trace.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index c3c7f1f85c53..1bc39f674f11 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -1066,7 +1066,9 @@ static size_t btf_struct_scnprintf(const struct btf_type *type, struct btf *btf,
 		return 0;
 
 	/* pretty print the struct data here */
-	if (btf_dump__dump_type_data(btf_dump, type_id, arg->augmented.args->value, type->size, &dump_data_opts) == 0)
+	if (btf_dump__dump_type_data(btf_dump, type_id,
+				     arg->augmented.args->value,
+				     type->size, &dump_data_opts) <= 0)
 		return 0;
 
 	consumed = sizeof(*augmented_arg) + augmented_arg->size;
-- 
2.55.0