[PATCH 6/8] Mdmonitor: Refactor check_one_sharer() for better error handling

[Mateusz Grzonka <mateusz.grzonka@xxxxxxxxx>]

Also check if autorebuild.pid is a symlink, which we shouldn't accept.

Signed-off-by: Mateusz Grzonka <mateusz.grzonka@xxxxxxxxx>
---
 Monitor.c | 89 ++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 62 insertions(+), 27 deletions(-)

diff --git a/Monitor.c b/Monitor.c
index 14a2dfe5..44918184 100644
--- a/Monitor.c
+++ b/Monitor.c
@@ -32,6 +32,7 @@
 #include	<libudev.h>
 #endif
 
+#define TASK_COMM_LEN 16
 #define EVENT_NAME_MAX 32
 #define AUTOREBUILD_PID_PATH MDMON_DIR "/autorebuild.pid"
 
@@ -224,7 +225,7 @@ int Monitor(struct mddev_dev *devlist,
 	info.hostname[sizeof(info.hostname) - 1] = '\0';
 
 	if (share){
-		if (check_one_sharer(c->scan))
+		if (check_one_sharer(c->scan) == 2)
 			return 1;
 	}
 
@@ -406,39 +407,73 @@ static int make_daemon(char *pidfile)
 	return -1;
 }
 
+/*
+ * check_one_sharer() - Checks for other mdmon processes running.
+ *
+ * Return:
+ * 0 - no other processes running,
+ * 1 - warning,
+ * 2 - error, or when scan mode is enabled, and one mdmon process already exists
+ */
 static int check_one_sharer(int scan)
 {
 	int pid;
-	FILE *comm_fp;
-	FILE *fp;
+	FILE *fp, *comm_fp;
 	char comm_path[PATH_MAX];
-	char path[PATH_MAX];
-	char comm[20];
-
-	sprintf(path, "%s/autorebuild.pid", MDMON_DIR);
-	fp = fopen(path, "r");
-	if (fp) {
-		if (fscanf(fp, "%d", &pid) != 1)
-			pid = -1;
-		snprintf(comm_path, sizeof(comm_path),
-			 "/proc/%d/comm", pid);
-		comm_fp = fopen(comm_path, "r");
-		if (comm_fp) {
-			if (fscanf(comm_fp, "%19s", comm) &&
-			    strncmp(basename(comm), Name, strlen(Name)) == 0) {
-				if (scan) {
-					pr_err("Only one autorebuild process allowed in scan mode, aborting\n");
-					fclose(comm_fp);
-					fclose(fp);
-					return 1;
-				} else {
-					pr_err("Warning: One autorebuild process already running.\n");
-				}
-			}
+	char comm[TASK_COMM_LEN];
+
+	if (!is_directory(MDMON_DIR)) {
+		pr_err("%s is not a regular directory.\n", MDMON_DIR);
+		return 2;
+	}
+
+	if (access(AUTOREBUILD_PID_PATH, F_OK) != 0)
+		return 0;
+
+	if (!is_file(AUTOREBUILD_PID_PATH)) {
+		pr_err("%s is not a regular file.\n", AUTOREBUILD_PID_PATH);
+		return 2;
+	}
+
+	fp = fopen(AUTOREBUILD_PID_PATH, "r");
+	if (!fp) {
+		pr_err("Cannot open %s file.\n", AUTOREBUILD_PID_PATH);
+		return 2;
+	}
+
+	if (fscanf(fp, "%d", &pid) != 1) {
+		pr_err("Cannot read pid from %s file.\n", AUTOREBUILD_PID_PATH);
+		fclose(fp);
+		return 2;
+	}
+
+	snprintf(comm_path, sizeof(comm_path), "/proc/%d/comm", pid);
+
+	comm_fp = fopen(comm_path, "r");
+	if (!comm_fp) {
+		dprintf("Warning: Cannot open %s, continuing\n", comm_path);
+		fclose(fp);
+		return 1;
+	}
+
+	if (fscanf(comm_fp, "%15s", comm) == 0) {
+		dprintf("Warning: Cannot read comm from %s, continuing\n", comm_path);
+		fclose(comm_fp);
+		fclose(fp);
+		return 1;
+	}
+
+	if (strncmp(basename(comm), Name, strlen(Name)) == 0) {
+		if (scan) {
+			pr_err("Only one autorebuild process allowed in scan mode, aborting\n");
 			fclose(comm_fp);
+			fclose(fp);
+			return 2;
 		}
-		fclose(fp);
+		pr_err("Warning: One autorebuild process already running.\n");
 	}
+	fclose(comm_fp);
+	fclose(fp);
 	return 0;
 }
 
-- 
2.26.2