[PATCH v2 03/16] fsnotify: generate pre-content permission event on open

Josef Bacik
2024-08-08T19:28:22Z

From: Amir Goldstein <amir73il@gmail.com>

FS_PRE_ACCESS or FS_PRE_MODIFY will be generated on open depending on
file open mode. The pre-content event will be generated 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 | 9 +++++++++
include/linux/fsnotify.h | 10 +++++++++-
2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 3a4c40e12f78..c16487e3742d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3735,6 +3735,15 @@ static int do_open(struct nameidata *nd,
}
if (do_truncate)
mnt_drop_write(nd->path.mnt);
+
+ /*
+ * 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.
+ */
+ if (!error)
+ error = fsnotify_file_perm(file, MAY_OPEN);
+
return error;
}

diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index 028ce807805a..a28daf136fea 100644
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -168,6 +168,10 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
fsnotify_mask = FS_PRE_MODIFY;
else if (perm_mask & MAY_READ)
fsnotify_mask = FS_PRE_ACCESS;
+ else if (perm_mask & MAY_OPEN && file->f_mode & FMODE_WRITER)
+ fsnotify_mask = FS_PRE_MODIFY;
+ else if (perm_mask & MAY_OPEN)
+ fsnotify_mask = FS_PRE_ACCESS;
else
return 0;

@@ -176,10 +180,14 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,

/*
* fsnotify_file_perm - permission hook before file access
+ *
+ * Called from read()/write() with perm_mask MAY_READ/MAY_WRITE.
+ * Called from open() with MAY_OPEN without sb_writers held and after the file
+ * was truncated. Note that this is a different event from fsnotify_open_perm().
*/
static inline int fsnotify_file_perm(struct file *file, int perm_mask)
{
- return fsnotify_file_area_perm(file, perm_mask, NULL, 0);
+ return fsnotify_file_area_perm(file, perm_mask, &file->f_pos, 0);
}

/*
--
2.43.0