[PATCH] nat: linux-namespaces: Also enter user namespace

[benjamin@sipsolutions.net]

From: Benjamin Berg <benjamin@sipsolutions.net>

The use of user namespaces is required for normal users to use mount
namespaces. Also entering the user namespace means that a normal user
can debug processes created that way.
---
 gdb/nat/linux-namespaces.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/gdb/nat/linux-namespaces.c b/gdb/nat/linux-namespaces.c
index 4b1fee18425..95277b403d7 100644
--- a/gdb/nat/linux-namespaces.c
+++ b/gdb/nat/linux-namespaces.c
@@ -880,11 +880,12 @@ enum mnsh_fs_code
 static enum mnsh_fs_code
 linux_mntns_access_fs (pid_t pid)
 {
-  struct linux_ns *ns;
+  struct linux_ns *ns, *ns_user;
   struct stat sb;
   struct linux_mnsh *helper;
   ssize_t size;
-  int fd;
+  int fd, fd_user = -1;
+  int result, error;
 
   if (pid == getpid ())
     return MNSH_FS_DIRECT;
@@ -901,6 +902,8 @@ linux_mntns_access_fs (pid_t pid)
     {
       int save_errno = errno;
       close (fd);
+      if (fd_user >= 0)
+	close (fd_user);
       errno = save_errno;
     };
 
@@ -910,13 +913,23 @@ linux_mntns_access_fs (pid_t pid)
   if (sb.st_ino == ns->id)
     return MNSH_FS_DIRECT;
 
+  ns_user = linux_ns_get_namespace (LINUX_NS_USER);
+  if (ns_user != NULL)
+    fd_user = gdb_open_cloexec (linux_ns_filename (ns_user, pid), O_RDONLY, 0).release ();
+
   helper = linux_mntns_get_helper ();
   if (helper == NULL)
     return MNSH_FS_ERROR;
 
   if (sb.st_ino != helper->nsid)
     {
-      int result, error;
+      /* Try to enter user namespace */
+      if (fd_user >= 0)
+	{
+	  mnsh_send_setns (helper, fd_user, 0);
+	  if (mnsh_recv_int (helper, &result, &error) != 0)
+	    warning (_("Could not enter user namespace"));
+	}
 
       size = mnsh_send_setns (helper, fd, 0);
       if (size < 0)
-- 
2.39.2