Patch "exec: Simplify unshare_files" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    exec: Simplify unshare_files

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     exec-simplify-unshare_files.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit d3fa9dc5e60e3e3955f04b51b6cac20d4ca7fa3c
Author: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Date:   Fri Nov 20 17:14:19 2020 -0600

    exec: Simplify unshare_files
    
    [ Upstream commit 1f702603e7125a390b5cdf5ce00539781cfcc86a ]
    
    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.
    
    Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
    v1: https://lkml.kernel.org/r/20200817220425.9389-2-ebiederm@xxxxxxxxxxxx
    Link: https://lkml.kernel.org/r/20201120231441.29911-2-ebiederm@xxxxxxxxxxxx
    Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/coredump.c b/fs/coredump.c
index 9d91e831ed0b2..7b085975ea163 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -590,7 +590,6 @@ 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;
@@ -797,11 +796,9 @@ 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 42952cf90f4af..d5c8f085235bc 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1245,7 +1245,6 @@ 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 */
@@ -1266,11 +1265,9 @@ 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 f1a99d3e55707..b32ab2163dc2d 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 633b0af1d1a73..8b8a5a172b158 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -3077,21 +3077,21 @@ 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;
 }