[PATCH v6 06/17] fsnotify: generate pre-content permission event on open

[Josef Bacik <josef@toxicpanda.com>]

From: Amir Goldstein <amir73il@gmail.com>

Generate pre-content event on open in addition to FS_OPEN_PERM,
but without sb_writers held and after file was truncated
in case file was opened with O_CREAT and/or O_TRUNC.

The event will have a range info of [0..0] to provide an opportunity
to fill entire file content on open.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/namei.c               | 10 +++++++++-
 include/linux/fsnotify.h |  4 +++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 4a4a22a08ac2..b49fb1f80c0c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3782,7 +3782,15 @@ static int do_open(struct nameidata *nd,
 	}
 	if (do_truncate)
 		mnt_drop_write(nd->path.mnt);
-	return error;
+	if (error)
+		return error;
+
+	/*
+	 * This permission hook is different than fsnotify_open_perm() hook.
+	 * This is a pre-content hook that is called without sb_writers held
+	 * and after the file was truncated.
+	 */
+	return fsnotify_file_area_perm(file, MAY_OPEN, &file->f_pos, 0);
 }
 
 /**
diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index 22150e5797c5..1e87a54b88b6 100644
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -171,6 +171,8 @@ static inline int fsnotify_pre_content(const struct file *file,
 
 /*
  * fsnotify_file_area_perm - permission hook before access of file range
+ *
+ * Called post open with access range [0..0].
  */
 static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
 					  const loff_t *ppos, size_t count)
@@ -185,7 +187,7 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
 	/*
 	 * read()/write and other types of access generate pre-content events.
 	 */
-	if (perm_mask & (MAY_READ | MAY_WRITE | MAY_ACCESS)) {
+	if (perm_mask & (MAY_READ | MAY_WRITE | MAY_ACCESS | MAY_OPEN)) {
 		int ret = fsnotify_pre_content(file, ppos, count);
 
 		if (ret)
-- 
2.43.0