linux-kernel - [RFC][PATCH 2/3] exec: Simplify unshare

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Date:   Sun, 16 Sep 2018 19:40:43 +0200
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Jeff Layton <jlayton@...nel.org>
Cc:     viro@...iv.linux.org.uk, berrange@...hat.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Oleg Nesterov <oleg@...hat.com>
Subject: [RFC][PATCH 2/3] exec: Simplify unshare_files


Now that exec calls unshare_files after the point of no return there
is no reason to return displaced.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.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 1e2c87acac9b..968ee5744bf9 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -546,7 +546,6 @@ void do_coredump(const siginfo_t *siginfo)
 	struct cred *cred;
 	int retval = 0;
 	int ispipe;
-	struct files_struct *displaced;
 	/* require nonrelative corefile path and be extra careful */
 	bool need_suid_safe = false;
 	bool core_dumped = false;
@@ -747,11 +746,9 @@ void do_coredump(const 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()) {
 		file_start_write(cprm.file);
 		core_dumped = binfmt->core_dump(&cprm);
diff --git a/fs/exec.c b/fs/exec.c
index 6f6167ec08eb..7eeffa7d98c6 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1252,7 +1252,6 @@ 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;
 
 	/*
@@ -1292,11 +1291,9 @@ int flush_old_exec(struct linux_binprm * bprm)
 	flush_thread();
 	current->personality &= ~bprm->per_clear;
 
-	retval = unshare_files(&displaced);
+	retval = unshare_files();
 	if (retval)
 		goto out;
-	if (displaced)
-		put_files_struct(displaced);
 
 	/*
 	 * We have to apply CLOEXEC before we change whether the process is
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 41615f38bcff..e65379336c4c 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -108,7 +108,7 @@ 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 *, 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 d896e9ca38b0..a06a609075eb 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2564,21 +2564,21 @@ 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 *files, *copy = NULL;
 	int error;
 
 	error = unshare_fd(CLONE_FILES, &copy);
-	if (error || !copy) {
-		*displaced = NULL;
+	if (error || !copy)
 		return error;
-	}
-	*displaced = task->files;
+
+	files = task->files;
 	task_lock(task);
 	task->files = copy;
 	task_unlock(task);
+	put_files_struct(files);
 	return 0;
 }
 
-- 
2.17.1