Added mutex to permissions checks to avoid inconsistent permission checking

/proc/pid/exe already seems to be a link to the absolute path to the
executable. This fixes bugs related to containerised applications.

src/perm_permissions_table.c

@@ -207,6 +207,9 @@ void destroy_perm_permissions_table(void) { sqlite3_close(perm_database); }
  */
 access_t check_perm_access_noparent(const char *filename,
                                     struct process_info pi) {
+  if (pi.name == NULL)
+    return NDEF;
+
   access_t ret = NDEF;
   sqlite3_stmt *stmt = NULL;
   const char *sql = "SELECT mode FROM permissions WHERE executable = ?1 "

src/proc_operations.c

@@ -8,8 +8,10 @@
 
 #include "proc_operations.h"
 #include <linux/limits.h>
+#include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 /**
  * @brief Returns the PID of the main thread (i.e., the process ID) of the
@@ -54,11 +56,38 @@ char *get_process_name_by_pid(const int pid) {
   char path[1024];
   sprintf(path, "/proc/%d/exe", pid);
 
-  char *name = realpath(path, NULL);
+  size_t size = 128;
+  char *name = malloc(size);
   if (name == NULL) {
     fprintf(stderr, "Could not get process name by pid %d", pid);
     perror("");
+    return NULL;
   }
+
+  while (1) {
+    ssize_t len = readlink(path, name, size);
+
+    if (len == -1) {
+      fprintf(stderr, "Could not get process name by pid %d", pid);
+      perror("");
+      free(name);
+      return NULL;
+    }
+    if ((size_t)len >= size) {
+      size *= 2;
+      char *new_name = realloc(name, size);
+      if (!new_name) {
+        free(name);
+        return NULL;
+      }
+      name = new_name;
+    } else {
+      // readlink does not set the null character
+      name[len] = 0;
+      break;
+    }
+  }
+
   return name;
 }
 

src/temp_permissions_table.c

@@ -254,6 +254,8 @@ access_t check_temp_access(const char *filename, struct process_info pi) {
  */
 int set_temp_access(const char *filename, struct process_info pi,
                     set_mode_t mode) {
+  if (pi.PID == 0)
+    return NDEF;
   pthread_rwlock_wrlock(&temp_permissions_table_lock);
   struct temp_process_permissions *permission_entry =
       get(&temp_permissions_table, pi.PID);

src/ui-socket.c

@@ -30,6 +30,8 @@
 #define DIALOGUE_NO 1
 #define DIALOGUE_PERM 2
 
+pthread_mutex_t access_check_mutex = PTHREAD_MUTEX_INITIALIZER;
+
 struct dialogue_response {
   access_t decision;
   char *filename;
@@ -127,6 +129,7 @@ struct dialogue_response ask_access(const char *filename,
   }
 
   int dialogue_exit_code = WEXITSTATUS(pclose(fp));
+
   fprintf(stderr, "dialogue wrote out %s\n", first(&dialogue_output));
   fprintf(stderr, "dialogue returned %d\n", dialogue_exit_code);
 
@@ -172,6 +175,7 @@ struct dialogue_response ask_access(const char *filename,
 int interactive_access(const char *filename, struct process_info proc_info,
                        int opts) {
   char *real_path = real_filename(filename);
+  pthread_mutex_lock(&access_check_mutex);
 
   access_t access = check_temp_access(real_path, proc_info);
   if (access == ALLOW) {
@@ -180,6 +184,7 @@ int interactive_access(const char *filename, struct process_info proc_info,
             "permission table.\n",
             proc_info.name);
     free(real_path);
+    pthread_mutex_unlock(&access_check_mutex);
     return 1;
   }
   if (access == DENY) {
@@ -188,6 +193,7 @@ int interactive_access(const char *filename, struct process_info proc_info,
             "permission table.\n",
             proc_info.name);
     free(real_path);
+    pthread_mutex_unlock(&access_check_mutex);
     return 0;
   }
 
@@ -198,6 +204,7 @@ int interactive_access(const char *filename, struct process_info proc_info,
             "permission table.\n",
             proc_info.name);
     free(real_path);
+    pthread_mutex_unlock(&access_check_mutex);
     return 1;
   }
   if (access == DENY) {
@@ -206,6 +213,7 @@ int interactive_access(const char *filename, struct process_info proc_info,
             "permission table.\n",
             proc_info.name);
     free(real_path);
+    pthread_mutex_unlock(&access_check_mutex);
     return 0;
   }
 
@@ -216,12 +224,14 @@ int interactive_access(const char *filename, struct process_info proc_info,
     fprintf(stderr, "Permission granted permanently to %s.\n", proc_info.name);
     set_perm_access(real_path, proc_info, SET_ALLOW);
     free(real_path);
+    pthread_mutex_unlock(&access_check_mutex);
     return 1;
   }
   if (opts & GRANT_TEMP) {
     fprintf(stderr, "Permission granted temporarily to %s.\n", proc_info.name);
     set_temp_access(real_path, proc_info, SET_ALLOW);
     free(real_path);
+    pthread_mutex_unlock(&access_check_mutex);
     return 1;
   }
 
@@ -245,43 +255,36 @@ int interactive_access(const char *filename, struct process_info proc_info,
   real_path = real_filename(response.filename);
   free(response.filename);
 
+  int ret = 0;
+
   if (response.decision == ALLOW) {
     fprintf(stderr,
             "Permission granted permanently to %s based on zenty response.\n",
             proc_info.name);
     set_perm_access(real_path, proc_info, SET_ALLOW);
-    free(real_path);
-    return 1;
-  }
-
-  if (response.decision == ALLOW_TEMP) {
+    ret = 1;
+  } else if (response.decision == ALLOW_TEMP) {
     fprintf(stderr,
             "Permission granted temporarily to %s based on zenty response.\n",
             proc_info.name);
     set_temp_access(real_path, proc_info, SET_ALLOW);
-    free(real_path);
-    return 1;
-  }
-
-  if (response.decision == DENY_TEMP) {
+    ret = 1;
+  } else if (response.decision == DENY_TEMP) {
     fprintf(stderr,
             "Permission denied temporarily to %s based on zenty response.\n",
             proc_info.name);
     set_temp_access(real_path, proc_info, SET_DENY);
-    free(real_path);
-    return 0;
-  }
-
-  if (response.decision == DENY) {
+    ret = 0;
+  } else if (response.decision == DENY) {
     fprintf(stderr,
             "Permission denied permanently to %s based on zenty response.\n",
             proc_info.name);
     set_perm_access(real_path, proc_info, SET_DENY);
-    free(real_path);
-    return 0;
+    ret = 0;
   }
+  pthread_mutex_unlock(&access_check_mutex);
 
   free(real_path);
   // deny on unknown options.
-  return 0;
+  return ret;
 }