Fix exec_paths through fakeroot or chroot

If file_name_exec is not given, check_hashbang will try to locate the
file. If argv[0] contains a '/', the file path is assumed to be
absolute and it will try to open the file. Otherwise, the file is
searched in the PATH. In either case, the resulting file identity port
is compared to the identity port of the original file handle passed to
check_hashbang.

exec_paths_exec.patch explicitly provides the script files path in
file_name_exec. According to the comment, if this path is provided, it
is assumed to be the path to the script file and no attempt at
locating the script file is done. However, the identity ports are
still compared. This cannot succeed if fakeroot or chroot is used,
because the process doing the exec and thus the initial file lookup is
running in the chrooted environment, while the exec server is not.

Fix this by skipping the identity test if file_name_exec is provided.

* exec/hashexec.c (check_hashbang): Skip the file identity test if the
file_name_exec is provided.

1 files changed, 51 insertions, 42 deletions

diff --git a/exec/hashexec.c b/exec/hashexec.c
index a7368390..71c02386 100644
--- a/exec/hashexec.c
+++ b/exec/hashexec.c
@@ -230,11 +230,12 @@ check_hashbang (struct execdata *e,
 	  else if (! (flags & EXEC_SECURE))
 	    {
 	      /* Try to figure out the file's name.  If FILE_NAME_EXEC
-		 is not NULL, then it's the file's name.  Otherwise we
-		 guess that if ARGV[0] contains a slash, it might be
-		 the name of the file; and that if it contains no slash,
-		 looking for files named by ARGV[0] in the `PATH'
-		 environment variable might find it.  */
+		 is not NULL and not the empty string, then it's the
+		 file's name.  Otherwise we guess that if ARGV[0]
+		 contains a slash, it might be the name of the file;
+		 and that if it contains no slash, looking for files
+		 named by ARGV[0] in the `PATH' environment variable
+		 might find it.  */
 
 	      error_t error;
 	      char *name;
@@ -270,51 +271,59 @@ check_hashbang (struct execdata *e,
 		  return err;
 		}
 
-	      error = io_identity (file, &fileid, &filefsid, &fileno);
-	      if (error)
-		goto out;
-	      mach_port_deallocate (mach_task_self (), filefsid);
-
-	      if (memchr (argv, '\0', argvlen) == NULL)
-		{
-		  name = alloca (argvlen + 1);
-		  memcpy (name, argv, argvlen);
-		  name[argvlen] = '\0';
-		}
-	      else
-		name = argv;
-
 	      if (file_name_exec && file_name_exec[0] != '\0')
-		error = lookup (name = file_name_exec, 0, &name_file);
-	      else if (strchr (name, '/') != NULL)
-		error = lookup (name, 0, &name_file);
-	      else if ((error = hurd_catch_signal
-			(sigmask (SIGBUS) | sigmask (SIGSEGV),
-			 (vm_address_t) envp, (vm_address_t) envp + envplen,
-			 &search_path, SIG_ERR)))
-		name_file = MACH_PORT_NULL;
-
-	      if (!error && name_file != MACH_PORT_NULL)
+		name = file_name_exec;
+	      else
 		{
-		  mach_port_t id, fsid;
-		  ino_t ino;
-		  error = io_identity (name_file, &id, &fsid, &ino);
-		  mach_port_deallocate (mach_task_self (), name_file);
-		  if (!error)
+		  /* Try to locate the file.  */
+		  error = io_identity (file, &fileid, &filefsid, &fileno);
+		  if (error)
+		    goto out;
+		  mach_port_deallocate (mach_task_self (), filefsid);
+
+		  if (memchr (argv, '\0', argvlen) == NULL)
 		    {
-		      mach_port_deallocate (mach_task_self (), fsid);
-		      mach_port_deallocate (mach_task_self (), id);
+		      name = alloca (argvlen + 1);
+		      memcpy (name, argv, argvlen);
+		      name[argvlen] = '\0';
 		    }
-		  if (!error && id == fileid)
+		  else
+		    name = argv;
+
+		  if (strchr (name, '/') != NULL)
+		    error = lookup (name, 0, &name_file);
+		  else if ((error = hurd_catch_signal
+			    (sigmask (SIGBUS) | sigmask (SIGSEGV),
+			     (vm_address_t) envp, (vm_address_t) envp + envplen,
+			     &search_path, SIG_ERR)))
+		    name_file = MACH_PORT_NULL;
+
+		  /* See whether we found the right file.  */
+		  if (!error && name_file != MACH_PORT_NULL)
 		    {
-		      file_name = name;
-		      free_file_name = free_name;
+		      mach_port_t id, fsid;
+		      ino_t ino;
+		      error = io_identity (name_file, &id, &fsid, &ino);
+		      mach_port_deallocate (mach_task_self (), name_file);
+		      if (!error)
+			{
+			  mach_port_deallocate (mach_task_self (), fsid);
+			  mach_port_deallocate (mach_task_self (), id);
+			  if (id != fileid)
+			    error = 1;
+			}
 		    }
-		  else if (free_name)
-		    free (name);
+
+		  mach_port_deallocate (mach_task_self (), fileid);
 		}
 
-	      mach_port_deallocate (mach_task_self (), fileid);
+	      if (!error)
+		{
+		  file_name = name;
+		  free_file_name = free_name;
+		}
+	      else if (free_name)
+		free (name);
 	    }
 
 	  if (file_name == NULL)