user database: improve error strings and checks

src/lib/firejail_user.c

@@ -29,6 +29,7 @@
 #include "../include/firejail_user.h"
 #include <sys/types.h>
 #include <pwd.h>
+#include <errno.h>
 
 #define MAXBUF 4098
 
@@ -113,15 +114,22 @@ int firejail_user_check(const char *name) {
 
  // check file existence
  char *fname = get_fname();
+ assert(fname);
  if (access(fname, F_OK)) {
- free(fname);
- return 1; // assume the user doesn't care about access checking
+ if (errno == ENOENT) { // assume the user doesn't care about access checking
+ free(fname);
+ return 1;
+ }
+ else { // for example no search permission on SYSCONFDIR
+ fprintf(stderr, "Error: cannot access %s\n", fname);
+ perror("access");
+ exit(1);
+ }
  }
 
  FILE *fp = fopen(fname, "r");
  if (!fp) {
- fprintf(stderr, "Error: cannot open %s for reading. "
- "See \"man firejail-users\" for more information about this file.\n", fname);
+ fprintf(stderr, "Error: cannot read %s\n", fname);
  perror("fopen");
  exit(1);
  }
@@ -166,6 +174,7 @@ void firejail_user_add(const char *name) {
  if (access(fname, F_OK) == 0) {
  if (firejail_user_check(name)) {
  printf("User %s already in the database\n", name);
+ free(fname);
  return;
  }
  }