[PATCH stalld 48/52] stalld: guard nextline() returns in sched_debug parsing

nextline() returns NULL when the input lacks a trailing newline,
which happens if sched_debug output is truncated. Both
detect_task_format() and parse_task_lines() pass the result directly
to string helpers that dereference it, causing a NULL pointer fault.

Add NULL checks after every nextline() call. In detect_task_format()
the daemon cannot function without a valid format, so it calls die().
In parse_task_lines() a truncated buffer simply means no more tasks
to parse, so the function returns the count collected so far. Also
remove the unreachable exit() after die() in the TASK_MARKER check.

Signed-off-by: Wander Lairson Costa <[email protected]>
---
 src/sched_debug.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/src/sched_debug.c b/src/sched_debug.c
index f481bb2..7d79255 100644
--- a/src/sched_debug.c
+++ b/src/sched_debug.c
@@ -233,13 +233,13 @@ static int detect_task_format(void)
 
 	/* find the delimiter for task information */
 	ptr = strstr(buffer, TASK_MARKER);
-	if (ptr == NULL) {
+	if (ptr == NULL)
 		die("unable to find 'runnable tasks' in buffer, invalid input\n");
-		exit(-1);
-	}
 
 	/* move to the column header line */
 	ptr = nextline(ptr);
+	if (!ptr)
+		die("invalid file format: %s\n", config_sched_debug_path);
 	i = 0;
 
 	/*
@@ -386,13 +386,20 @@ static int parse_task_lines(char *buffer, struct task_info *task_info, int nr_en
 	line = ptr;
 
 	/* skip "runnable tasks:" */
- 	line = nextline(line);
+	line = nextline(line);
+	if (!line)
+		return 0;
 
 	/* skip header lines */
 	line = nextline(line);
+	if (!line)
+		return 0;
 
 	/* skip divider line */
 	line = nextline(line);
+	if (!line)
+		return 0;
+
 	/* at this point, line should point to the start of a task line */
 
 	/* now loop over the task info
@@ -415,6 +422,8 @@ static int parse_task_lines(char *buffer, struct task_info *task_info, int nr_en
 			(*ptr == 'R')) {
 			/* Go to the end of the line and ignore this task. */
 			line = nextline(line);
+			if (!line)
+				return 0;
 			continue;
 		}
 
@@ -429,6 +438,8 @@ static int parse_task_lines(char *buffer, struct task_info *task_info, int nr_en
 		if (config_task_format == NEW_TASK_FORMAT) {
 			if (*ptr == '>' || (*ptr != 'R' && *ptr != 'X')) {
 				line = nextline(line);
+				if (!line)
+					return 0;
 				continue;
 			}
 		}
@@ -436,7 +447,7 @@ static int parse_task_lines(char *buffer, struct task_info *task_info, int nr_en
 		/*
 		 * At this point we have a task line to record
 		 */
-		
+
 		/* get the task field */
 		ptr = skip2word(line, config_task_format_offsets.task);
 
@@ -485,6 +496,8 @@ static int parse_task_lines(char *buffer, struct task_info *task_info, int nr_en
 
 		/* move our line pointer to the next availble line */
 		line = nextline(line);
+		if (!line)
+			return 0;
 	}
 	return tasks;
 }
-- 
2.54.0