[stable/linux-6.6.y 1/3] fs: prepare for adding LSM blob to backing_file

[Cai Xinchen]

From: Amir Goldstein <amir73il@xxxxxxxxx>

1. The commit def3ae83da02
("fs: store real path instead of fake path in backing file f_path")
is not merged, The 6.6 LTS version accordingly operates on
&ff->real_path instead of &ff->user_path.

2. Mainline's file_free() does both the backing_file cleanup and the
kmem_cache_free() synchronously.  Linux 6.6.y defers the actual kfree()
to file_free_rcu() via call_rcu(), so only path_put() is done
synchronously in file_free().

original commit message:

In preparation to adding LSM blob to backing_file struct, factor out
helpers init_backing_file() and backing_file_free().

Cc: stable@xxxxxxxxxxxxxxx
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-unionfs@xxxxxxxxxxxxxxx
Cc: linux-erofs@xxxxxxxxxxxxxxxx
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Reviewed-by: Serge Hallyn <serge@xxxxxxxxxx>
[PM: use the term "LSM blob", fix comment style to match file]
Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx>
Signed-off-by: Cai Xinchen <caixinchen1@xxxxxxxxxx>
---
 fs/file_table.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index 234284ef72a9..b4c208a77153 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -72,11 +72,16 @@ static void file_free_rcu(struct rcu_head *head)
 		kmem_cache_free(filp_cachep, f);
 }
 
+static inline void backing_file_free(struct backing_file *ff)
+{
+	path_put(&ff->real_path);
+}
+
 static inline void file_free(struct file *f)
 {
 	security_file_free(f);
 	if (unlikely(f->f_mode & FMODE_BACKING))
-		path_put(backing_file_real_path(f));
+		backing_file_free(backing_file(f));
 	if (likely(!(f->f_mode & FMODE_NOACCOUNT)))
 		percpu_counter_dec(&nr_files);
 	call_rcu(&f->f_rcuhead, file_free_rcu);
@@ -252,6 +257,12 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
 	return f;
 }
 
+static int init_backing_file(struct backing_file *ff)
+{
+	memset(&ff->real_path, 0, sizeof(ff->real_path));
+	return 0;
+}
+
 /*
  * Variant of alloc_empty_file() that allocates a backing_file container
  * and doesn't check and modify nr_files.
@@ -274,7 +285,14 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
 		return ERR_PTR(error);
 	}
 
+	/* The f_mode flags must be set before fput(). */
 	ff->file.f_mode |= FMODE_BACKING | FMODE_NOACCOUNT;
+	error = init_backing_file(ff);
+	if (unlikely(error)) {
+		fput(&ff->file);
+		return ERR_PTR(error);
+	}
+
 	return &ff->file;
 }
 
-- 
2.18.0.huawei.25