merge #1100 from zackw: rework abstract X11 socket detection

2 files changed, 70 insertions, 50 deletions

diff --git a/README b/README
index 52c5f7dd2..e729b4580 100644
--- a/README
+++ b/README
@@ -104,7 +104,10 @@ valoq (https://github.com/valoq)
 Zack Weinberg (https://github.com/zackw)
         - removed libconnect
         - fixed memory corruption in noblacklist processing
-        - rework DISPLAY environment parsing, rework masking X11 sockets in /tmp/.X11-unix directory
+        - rework DISPLAY environment parsing
+        - rework masking X11 sockets in /tmp/.X11-unix directory
+        - rework xpra and xephyr detection
+        - rework abstract X11 socket detection
 Igor Bukanov (https://github.com/ibukanov)
         - found/fiixed privilege escalation in --hosts-file option
 Cat (https://github.com/ecat3)
diff --git a/src/firejail/x11.c b/src/firejail/x11.c
index f81a52b70..328ecce18 100644
--- a/src/firejail/x11.c
+++ b/src/firejail/x11.c
@@ -31,30 +31,85 @@
 #include <limits.h>
 int mask_x11_abstract_socket = 0;
 
+
+// Parse the DISPLAY environment variable and return a display number.
+// Returns -1 if DISPLAY is not set, or is set to anything other than :ddd.
+int x11_display(void) {
+        const char *display_str = getenv("DISPLAY");
+        char *endp;
+        unsigned long display;
+
+        if (!display_str) {
+                if (arg_debug)
+                        fputs("DISPLAY is not set\n", stderr);
+                return -1;
+        }
+
+        if (display_str[0] != ':' || display_str[1] < '0' || display_str[1] > '9') {
+                if (arg_debug)
+                        fprintf(stderr, "unsupported DISPLAY form '%s'\n", display_str);
+                return -1;
+        }
+
+        errno = 0;
+        display = strtoul(display_str+1, &endp, 10);
+        if (endp == display_str+1 || (*endp != '\0' && *endp != '.')) { // handling DISPLAY=:0 and also :0.0
+                if (arg_debug)
+                        fprintf(stderr, "unsupported DISPLAY form '%s'\n", display_str);
+                return -1;
+        }
+        if (errno || display > (unsigned long)INT_MAX) {
+                if (arg_debug)
+                        fprintf(stderr, "display number %s is outside the valid range\n",
+                                display_str+1);
+                return -1;
+        }
+
+        if (arg_debug)
+                fprintf(stderr, "DISPLAY=%s parsed as %lu\n", display_str, display);
+
+        return (int)display;
+}
+
+
 #ifdef HAVE_X11
 // check for X11 abstract sockets
 static int x11_abstract_sockets_present(void) {
-        char *path;
 
         EUID_ROOT(); // grsecurity fix
         FILE *fp = fopen("/proc/net/unix", "r");
-        EUID_USER();
-
         if (!fp)
                 errExit("fopen");
+        EUID_USER();
+
+        char *linebuf = 0;
+        size_t bufsz = 0;
+        int found = 0;
+        errno = 0;
 
-        while (fscanf(fp, "%*s %*s %*s %*s %*s %*s %*s %ms\n", &path) != EOF) {
-                if (path && strncmp(path, "@/tmp/.X11-unix/", 16) == 0) {
-                        free(path);
-                        fclose(fp);
-                        return 1;
+        for (;;) {
+                if (getline(&linebuf, &bufsz, fp) == -1) {
+                        if (errno)
+                                errExit("getline");
+                        break;
+                }
+                // The last space-separated field in 'linebuf' is the
+                // pathname of the socket.  Abstract sockets' pathnames
+                // all begin with '@/', normal ones begin with '/'.
+                char *p = strrchr(linebuf, ' ');
+                if (!p) {
+                        fputs("error parsing /proc/net/unix\n", stderr);
+                        exit(1);
+                }
+                if (strncmp(p+1, "@/tmp/.X11-unix/", 16) == 0) {
+                        found = 1;
+                        break;
                 }
         }
 
-        free(path);
+        free(linebuf);
         fclose(fp);
-
-        return 0;
+        return found;
 }
 
 static int random_display_number(void) {
@@ -84,44 +139,6 @@ static int random_display_number(void) {
 #endif
 
 
-// Parse the DISPLAY environment variable and return a display number.
-// Returns -1 if DISPLAY is not set, or is set to anything other than :ddd.
-int x11_display(void) {
-        const char *display_str = getenv("DISPLAY");
-        char *endp;
-        unsigned long display;
-
-        if (!display_str) {
-                if (arg_debug)
-                        fputs("DISPLAY is not set\n", stderr);
-                return -1;
-        }
-
-        if (display_str[0] != ':' || display_str[1] < '0' || display_str[1] > '9') {
-                if (arg_debug)
-                        fprintf(stderr, "unsupported DISPLAY form '%s'\n", display_str);
-                return -1;
-        }
-
-        errno = 0;
-        display = strtoul(display_str+1, &endp, 10);
-        if (endp == display_str+1 || (*endp != '\0' && *endp != '.')) { // handling DISPLAY=:0 and also :0.0
-                if (arg_debug)
-                        fprintf(stderr, "unsupported DISPLAY form '%s'\n", display_str);
-                return -1;
-        }
-        if (errno || display > (unsigned long)INT_MAX) {
-                if (arg_debug)
-                        fprintf(stderr, "display number %s is outside the valid range\n",
-                                display_str+1);
-                return -1;
-        }
-
-        if (arg_debug)
-                fprintf(stderr, "DISPLAY=%s parsed as %lu\n", display_str, display);
-
-        return (int)display;
-}
 
 void fs_x11(void) {
 #ifdef HAVE_X11