From ca925a740afc0a377946d72680c40f9e7719e4ec Mon Sep 17 00:00:00 2001
From: Zhang Ning <832666+zhangn1985@users.noreply.github.com>
Date: Sun, 27 Jan 2019 18:37:00 +0800
Subject: [PATCH] fs/file_table: split fget_light

due to systemd updated, sun8i kernel doesn't compact to new systemd.
after check systemd code, it return -EBADF in below code:

https://github.com/systemd/systemd/blob/master/src/basic/fs-util.c#L804-L815

fstat on path fds (open with O_PATH).

after check sun8i kernel code, in fstat path, fget_light rectly returns
NULL on path fds (file->f_mode & FMODE_PATH).

on mainline kernel, fget_light is wraper function of __fget_light.
on fstat path, it uses __fget_light, doesn't check FMODE_PATH.

so follow mainline kernel, change the behavior of sun8i kernel.

test case:

int main(int argc, char **argv)
{
    int fd;
    struct stat previous_stat;

    fd =  open("/", O_CLOEXEC|O_NOFOLLOW|O_PATH);
    if (fd < 0) {
        printf("%d, %s\n", __LINE__,  strerror(errno));
         return -errno;
    }

    if(fstat(fd, &previous_stat) < 0) {

        printf("%d, %s\n", __LINE__, strerror(errno));
        return -errno;
    }
}

expect no error.

Signed-off-by: Zhang Ning <832666+zhangn1985@users.noreply.github.com>
---
 fs/file_table.c      | 11 ++++++++---
 fs/stat.c            |  2 +-
 include/linux/file.h |  1 +
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index a01710a6ff3b..afa758fc3764 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -322,7 +322,7 @@ EXPORT_SYMBOL(fget_raw);
  * The fput_needed flag returned by fget_light should be passed to the
  * corresponding fput_light.
  */
-struct file *fget_light(unsigned int fd, int *fput_needed)
+struct file *__fget_light(unsigned int fd, fmode_t mode, int *fput_needed)
 {
 	struct file *file;
 	struct files_struct *files = current->files;
@@ -330,13 +330,13 @@ struct file *fget_light(unsigned int fd, int *fput_needed)
 	*fput_needed = 0;
 	if (atomic_read(&files->count) == 1) {
 		file = fcheck_files(files, fd);
-		if (file && (file->f_mode & FMODE_PATH))
+		if (file && (file->f_mode & mode))
 			file = NULL;
 	} else {
 		rcu_read_lock();
 		file = fcheck_files(files, fd);
 		if (file) {
-			if (!(file->f_mode & FMODE_PATH) &&
+			if (!(file->f_mode & mode) &&
 			    atomic_long_inc_not_zero(&file->f_count))
 				*fput_needed = 1;
 			else
@@ -349,6 +349,11 @@ struct file *fget_light(unsigned int fd, int *fput_needed)
 	return file;
 }
 
+struct file *fget_light(unsigned int fd, int *fput_needed)
+{
+	return __fget_light(fd, FMODE_PATH, fput_needed);
+}
+
 struct file *fget_raw_light(unsigned int fd, int *fput_needed)
 {
 	struct file *file;
diff --git a/fs/stat.c b/fs/stat.c
index 88b36c770762..957d3348bfc8 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -58,7 +58,7 @@ EXPORT_SYMBOL(vfs_getattr);
 int vfs_fstat(unsigned int fd, struct kstat *stat)
 {
 	int fput_needed;
-	struct file *f = fget_light(fd, &fput_needed);
+	struct file *f = __fget_light(fd, 0, &fput_needed);
 	int error = -EBADF;
 
 	if (f) {
diff --git a/include/linux/file.h b/include/linux/file.h
index 58bf158c53d9..86fed86eeba2 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -28,6 +28,7 @@ static inline void fput_light(struct file *file, int fput_needed)
 
 extern struct file *fget(unsigned int fd);
 extern struct file *fget_light(unsigned int fd, int *fput_needed);
+extern struct file *__fget_light(unsigned int fd, fmode_t mode, int *fput_needed);
 extern struct file *fget_raw(unsigned int fd);
 extern struct file *fget_raw_light(unsigned int fd, int *fput_needed);
 extern void set_close_on_exec(unsigned int fd, int flag);