process start time verification to prevent PID reuse issues

Author: diffstorm

src/apps.h

@@ -57,6 +57,7 @@ typedef struct
     bool first_heartbeat; /**< Flag indicating whether the application has sent its first heartbeat. */
     int pid; /**< Process ID of the application. */
     time_t last_heartbeat; /**< Time when the last heartbeat was received from the application. */
+    time_t start_time; /**< Process start time in clock ticks since system boot. */
 } Application_t;
 
 typedef enum

src/process.c

@@ -42,6 +42,17 @@ bool process_is_running(int app_index)
     // Check if the application is running
     if(kill(pid, 0) == 0)
     {
+        // Verify process identity by checking start time to prevent PID reuse issues
+        time_t recorded_start_time = apps_get_array()[app_index].start_time;
+        time_t current_start_time = get_process_start_time(pid);
+        
+        if(current_start_time > 0 && recorded_start_time > 0 && current_start_time != recorded_start_time)
+        {
+            LOGE("Process %s PID %d has different start time (PID reused), treating as different process",
+                 get_app_name(app_index), pid);
+            return false;
+        }
+        
         return true;  // Process is running
     }
     else if(errno == EPERM)
@@ -121,6 +132,8 @@ void process_start(int app_index)
         apps[app_index].started = true;
         apps[app_index].first_heartbeat = false;
         apps[app_index].pid = pid;
+        // Record process start time from /proc/<pid>/stat
+        apps[app_index].start_time = get_process_start_time(pid);
         LOGI("Process %s started (PID %d): %s", apps[app_index].name, apps[app_index].pid, apps[app_index].cmd);
         // Use heartbeat module to update heartbeat time
         heartbeat_update_time(app_index);
@@ -220,6 +233,7 @@ void process_kill(int app_index)
         apps[app_index].started = false;
         apps[app_index].first_heartbeat = false;
         apps[app_index].pid = 0;
+        apps[app_index].start_time = 0;
     }
     else
     {

src/utils.c

@@ -47,6 +47,77 @@ long get_uptime()
     return s_info.uptime;
 }
 
+/**
+    @brief Gets the process start time from /proc/<pid>/stat in clock ticks since boot.
+    
+    According to proc(5), field 22 in /proc/<pid>/stat is the process start time
+    in clock ticks since system boot.
+    
+    @param pid Process ID to query.
+    @return Process start time in clock ticks since boot, or 0 on error.
+*/
+time_t get_process_start_time(int pid)
+{
+    char path[256];
+    char buffer[1024];
+    FILE *fp;
+    long start_time = 0;
+    
+    snprintf(path, sizeof(path), "/proc/%d/stat", pid);
+    
+    fp = fopen(path, "r");
+    if(fp == NULL)
+    {
+        return 0;
+    }
+    
+    if(fread(buffer, 1, sizeof(buffer) - 1, fp) <= 0)
+    {
+        fclose(fp);
+        return 0;
+    }
+    fclose(fp);
+    
+    buffer[sizeof(buffer) - 1] = '\0';
+    
+    // Find the last ')' in the command name (field 2 is command in parentheses)
+    // Then find field 22 (start time)
+    char *ptr = strrchr(buffer, ')');
+    if(ptr == NULL)
+    {
+        return 0;
+    }
+    
+    // Skip ')' and whitespace, then count 21 fields to get to field 22
+    ptr++; // Skip ')'
+    while(*ptr == ' ')
+    {
+        ptr++;
+    }
+    
+    // Count fields - skip first 21 fields
+    int field = 1;
+    while(field < 22 && *ptr != '\0')
+    {
+        while(*ptr == ' ')
+        {
+            ptr++;
+        }
+        while(*ptr != ' ' && *ptr != '\0')
+        {
+            ptr++;
+        }
+        field++;
+    }
+    
+    if(field == 22)
+    {
+        start_time = atol(ptr);
+    }
+    
+    return (time_t)start_time;
+}
+
 void delay_ms(int ms)
 {
     if(ms > 1000)

src/utils.h

@@ -94,6 +94,14 @@ char *pstrcpy(char *s1, const char *s2);
 */
 long get_uptime();
 
+/**
+    @brief Gets the process start time from /proc/<pid>/stat in clock ticks since boot.
+
+    @param pid Process ID to query.
+    @return Process start time in clock ticks since boot, or 0 on error.
+*/
+time_t get_process_start_time(int pid);
+
 /**
     @brief Waits for a specified number of milliseconds.