[RFC,1/3] exec: Move unshare_files down to avoid locks being dropped on exec.

Commit Message

Eric W. Biederman Sept. 16, 2018, 5:39 p.m. UTC

Signed-off-by: "Eric W. Biederman" <[e-mail]>
---
 fs/exec.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

Comments

Oleg Nesterov Sept. 17, 2018, 3:49 p.m. UTC | #1

On 09/16, Eric W. Biederman wrote:
>
> @@ -1291,6 +1292,12 @@ int flush_old_exec(struct linux_binprm * bprm)
>  	flush_thread();
>  	current->personality &= ~bprm->per_clear;
>
> +	retval = unshare_files(&displaced);

I was going to sugget basically the same changes, please feel free to add
my reviewed-by to 1-3.


Just for record. If we should really worry about unshare_files() failure
after de_thread() (imo we shouldn't), we can do another change:

	__do_execve_file:

		unshare_fd(CLONE_FILES, &bprm->unshared_copy);
		...


	flush_old_exec:

		de_thread();

		if (bprm->unshared_copy) {
			// now that we killed sub-threads recheck
			if (current->files->count > 1) {
				put_files_struct(current->files);
				current->files = bprm->unshared_copy;
			} else {
				put_files_struct(bprm->unshared_copy);
			}
				
		}

but again, I think your series is fine.

Oleg.

Patch

diff --git a/fs/exec.c b/fs/exec.c
index 1ebf6e5a521d..6f6167ec08eb 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1252,6 +1252,7 @@  void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
  */
 int flush_old_exec(struct linux_binprm * bprm)
 {
+	struct files_struct *displaced;
 	int retval;
 
 	/*
@@ -1291,6 +1292,12 @@  int flush_old_exec(struct linux_binprm * bprm)
 	flush_thread();
 	current->personality &= ~bprm->per_clear;
 
+	retval = unshare_files(&displaced);
+	if (retval)
+		goto out;
+	if (displaced)
+		put_files_struct(displaced);
+
 	/*
 	 * We have to apply CLOEXEC before we change whether the process is
 	 * dumpable (in setup_new_exec) to avoid a race with a process in userspace
@@ -1713,7 +1720,6 @@  static int __do_execve_file(int fd, struct filename *filename,
 {
 	char *pathbuf = NULL;
 	struct linux_binprm *bprm;
-	struct files_struct *displaced;
 	int retval;
 
 	if (IS_ERR(filename))
@@ -1735,14 +1741,10 @@  static int __do_execve_file(int fd, struct filename *filename,
 	 * further execve() calls fail. */
 	current->flags &= ~PF_NPROC_EXCEEDED;
 
-	retval = unshare_files(&displaced);
-	if (retval)
-		goto out_ret;
-
 	retval = -ENOMEM;
 	bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
 	if (!bprm)
-		goto out_files;
+		goto out_ret;
 
 	retval = prepare_bprm_creds(bprm);
 	if (retval)
@@ -1831,8 +1833,6 @@  static int __do_execve_file(int fd, struct filename *filename,
 	kfree(pathbuf);
 	if (filename)
 		putname(filename);
-	if (displaced)
-		put_files_struct(displaced);
 	return retval;
 
 out:
@@ -1849,9 +1849,6 @@  static int __do_execve_file(int fd, struct filename *filename,
 	free_bprm(bprm);
 	kfree(pathbuf);
 
-out_files:
-	if (displaced)
-		reset_files_struct(displaced);
 out_ret:
 	if (filename)
 		putname(filename);