[PATCH i-g-t 2/3] lib/drm_fdinfo: Ensure buffer is null terminated

[Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>]

From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Ensure buffer is null terminated at the point where the read ended and not
at the end of the whole buffer. Otherwise string parsing can stray into
un-initialised memory.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
 lib/igt_drm_fdinfo.c | 8 ++++----
 lib/igt_drm_fdinfo.h | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/lib/igt_drm_fdinfo.c b/lib/igt_drm_fdinfo.c
index b422f67a4ace..250d9e8917f2 100644
--- a/lib/igt_drm_fdinfo.c
+++ b/lib/igt_drm_fdinfo.c
@@ -44,12 +44,12 @@ static size_t read_fdinfo(char *buf, const size_t sz, int at, const char *name)
 	if (fd < 0)
 		return 0;
 
-	buf[sz - 1] = 0;
-	count = read(fd, buf, sz);
-	buf[sz - 1] = 0;
+	count = read(fd, buf, sz - 1);
+	if (count > 0)
+		buf[count - 1] = 0;
 	close(fd);
 
-	return count;
+	return count > 0 ? count : 0;
 }
 
 static int parse_engine(char *line, struct drm_client_fdinfo *info,
diff --git a/lib/igt_drm_fdinfo.h b/lib/igt_drm_fdinfo.h
index 5db63e28b07e..8759471615bd 100644
--- a/lib/igt_drm_fdinfo.h
+++ b/lib/igt_drm_fdinfo.h
@@ -46,7 +46,7 @@ struct drm_client_fdinfo {
  * igt_parse_drm_fdinfo: Parses the drm fdinfo file
  *
  * @drm_fd: DRM file descriptor
- * @info: Structure to populate with read data
+ * @info: Structure to populate with read data. Must be zeroed.
  *
  * Returns the number of valid drm fdinfo keys found or zero if not all
  * mandatory keys were present or no engines found.
@@ -58,7 +58,7 @@ unsigned int igt_parse_drm_fdinfo(int drm_fd, struct drm_client_fdinfo *info);
  *
  * @dir: File descriptor pointing to /proc/pid/fdinfo directory
  * @fd: String representation of the file descriptor number to parse.
- * @info: Structure to populate with read data
+ * @info: Structure to populate with read data. Must be zeroed.
  *
  * Returns the number of valid drm fdinfo keys found or zero if not all
  * mandatory keys were present or no engines found.
-- 
2.32.0