[PATCH] file: Call security_file_alloc() after initializing the filp

[Tianjia Zhang]

When developing a dedicated LSM module, we need to operate on the
file object within the LSM function, such as retrieving the path.
However, in `security_file_alloc()`, the passed-in `filp` is
only a valid pointer; the content of `filp` is completely
uninitialized and entirely random, which confuses the LSM function.

Therefore, it is necessary to call `security_file_alloc()` only
after the main fields of the `filp` object have been initialized.
This patch only moves the call to `security_file_alloc()` to the
end of the `init_file()` function.

Signed-off-by: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
---
 fs/file_table.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index 81c72576e548..e66531a629aa 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -156,11 +156,6 @@ static int init_file(struct file *f, int flags, const struct cred *cred)
 	int error;
 
 	f->f_cred = get_cred(cred);
-	error = security_file_alloc(f);
-	if (unlikely(error)) {
-		put_cred(f->f_cred);
-		return error;
-	}
 
 	spin_lock_init(&f->f_lock);
 	/*
@@ -202,6 +197,14 @@ static int init_file(struct file *f, int flags, const struct cred *cred)
 	 * They may be enabled later by fsnotify_open_perm_and_set_mode().
 	 */
 	file_set_fsnotify_mode(f, FMODE_NONOTIFY_PERM);
+
+	error = security_file_alloc(f);
+	if (unlikely(error)) {
+		mutex_destroy(&f->f_pos_lock);
+		put_cred(f->f_cred);
+		return error;
+	}
+
 	return 0;
 }
 
-- 
2.39.5 (Apple Git-154)