[PATCH 02/17] exec: Simplify unshare_files

[Eric W. Biederman]

Now that exec no longer needs to return the unshared files to their
previous value there is no reason to return displaced.

Instead when unshare_fd creates a copy of the file table, call
put_files_struct before returning from unshare_files.

Signed-off-by: "Eric W. Biederman" <ebied...@xmission.com>
---
 fs/coredump.c           |  5 +----
 fs/exec.c               |  5 +----
 include/linux/fdtable.h |  2 +-
 kernel/fork.c           | 12 ++++++------
 4 files changed, 9 insertions(+), 15 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 76e7c10edfc0..568d6e391082 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -585,7 +585,6 @@ void do_coredump(const kernel_siginfo_t *siginfo)
        int ispipe;
        size_t *argv = NULL;
        int argc = 0;
-       struct files_struct *displaced;
        /* require nonrelative corefile path and be extra careful */
        bool need_suid_safe = false;
        bool core_dumped = false;
@@ -791,11 +790,9 @@ void do_coredump(const kernel_siginfo_t *siginfo)
        }
 
        /* get us an unshared descriptor table; almost always a no-op */
-       retval = unshare_files(&displaced);
+       retval = unshare_files();
        if (retval)
                goto close_fail;
-       if (displaced)
-               put_files_struct(displaced);
        if (!dump_interrupted()) {
                /*
                 * umh disabled with CONFIG_STATIC_USERMODEHELPER_PATH="" would
diff --git a/fs/exec.c b/fs/exec.c
index 17c007bba712..9b723d2560d1 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1354,7 +1354,6 @@ void __set_task_comm(struct task_struct *tsk, const char 
*buf, bool exec)
 int begin_new_exec(struct linux_binprm * bprm)
 {
        struct task_struct *me = current;
-       struct files_struct *displaced;
        int retval;
 
        /* Once we are committed compute the creds */
@@ -1375,11 +1374,9 @@ int begin_new_exec(struct linux_binprm * bprm)
                goto out;
 
        /* Ensure the files table is not shared. */
-       retval = unshare_files(&displaced);
+       retval = unshare_files();
        if (retval)
                goto out;
-       if (displaced)
-               put_files_struct(displaced);
 
        /*
         * Must be called _before_ exec_mmap() as bprm->mm is
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index a32bf47c593e..f46a084b60b2 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -109,7 +109,7 @@ struct task_struct;
 struct files_struct *get_files_struct(struct task_struct *);
 void put_files_struct(struct files_struct *fs);
 void reset_files_struct(struct files_struct *);
-int unshare_files(struct files_struct **);
+int unshare_files(void);
 struct files_struct *dup_fd(struct files_struct *, unsigned, int *) 
__latent_entropy;
 void do_close_on_exec(struct files_struct *);
 int iterate_fd(struct files_struct *, unsigned,
diff --git a/kernel/fork.c b/kernel/fork.c
index 4d32190861bd..3049a41076f3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2995,21 +2995,21 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
  *     the exec layer of the kernel.
  */
 
-int unshare_files(struct files_struct **displaced)
+int unshare_files(void)
 {
        struct task_struct *task = current;
-       struct files_struct *copy = NULL;
+       struct files_struct *old, *copy = NULL;
        int error;
 
        error = unshare_fd(CLONE_FILES, NR_OPEN_MAX, &copy);
-       if (error || !copy) {
-               *displaced = NULL;
+       if (error || !copy)
                return error;
-       }
-       *displaced = task->files;
+
+       old = task->files;
        task_lock(task);
        task->files = copy;
        task_unlock(task);
+       put_files_struct(old);
        return 0;
 }
 
-- 
2.25.0