[PATCH 4.9 07/51] initramfs: finish fput() before accessing any binary from initramfs

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Lokesh Vutla <lokeshvutla@xxxxxx>


[ Upstream commit 08865514805d2de8e7002fa8149c5de3e391f412 ]

Commit 4a9d4b024a31 ("switch fput to task_work_add") implements a
schedule_work() for completing fput(), but did not guarantee calling
__fput() after unpacking initramfs.  Because of this, there is a
possibility that during boot a driver can see ETXTBSY when it tries to
load a binary from initramfs as fput() is still pending on that binary.

This patch makes sure that fput() is completed after unpacking initramfs
and removes the call to flush_delayed_fput() in kernel_init() which
happens very late after unpacking initramfs.

Link: http://lkml.kernel.org/r/20170201140540.22051-1-lokeshvutla@xxxxxx
Signed-off-by: Lokesh Vutla <lokeshvutla@xxxxxx>
Reported-by: Murali Karicheri <m-karicheri2@xxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Tero Kristo <t-kristo@xxxxxx>
Cc: Sekhar Nori <nsekhar@xxxxxx>
Cc: Nishanth Menon <nm@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 init/initramfs.c |    2 ++
 init/main.c      |    3 ---
 2 files changed, 2 insertions(+), 3 deletions(-)

--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -18,6 +18,7 @@
 #include <linux/dirent.h>
 #include <linux/syscalls.h>
 #include <linux/utime.h>
+#include <linux/file.h>
 
 static ssize_t __init xwrite(int fd, const char *p, size_t count)
 {
@@ -647,6 +648,7 @@ static int __init populate_rootfs(void)
 			printk(KERN_EMERG "Initramfs unpacking failed: %s\n", err);
 		free_initrd();
 #endif
+		flush_delayed_fput();
 		/*
 		 * Try loading default modules from initramfs.  This gives
 		 * us a chance to load before device_initcalls.
--- a/init/main.c
+++ b/init/main.c
@@ -70,7 +70,6 @@
 #include <linux/shmem_fs.h>
 #include <linux/slab.h>
 #include <linux/perf_event.h>
-#include <linux/file.h>
 #include <linux/ptrace.h>
 #include <linux/blkdev.h>
 #include <linux/elevator.h>
@@ -947,8 +946,6 @@ static int __ref kernel_init(void *unuse
 	system_state = SYSTEM_RUNNING;
 	numa_default_policy();
 
-	flush_delayed_fput();
-
 	rcu_end_inkernel_boot();
 
 	if (ramdisk_execute_command) {