[PATCH] kernfs: fix missing kernfs_iattr_rwsem locking

From: Ian Kent
Date: Sat Aug 05 2023 - 21:27:34 EST


When the kernfs_iattr_rwsem was introduced a case was missed.

The update of the kernfs directory node child count was also protected
by the kernfs_rwsem and needs to be included in the change so that the
child count (and so the inode n_link attribute) does not change while
holding the rwsem for read.

Fixes: 9caf696142 (kernfs: Introduce separate rwsem to protect inode
attributes)

Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
Reviewed-By: Imran Khan <imran.f.khan@xxxxxxxxxx>
Acked-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Cc: Anders Roxell <anders.roxell@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Eric Sandeen <sandeen@xxxxxxxxxxx>
---
fs/kernfs/dir.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 5a1a4af9d3d2..bf243015834e 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -383,9 +383,11 @@ static int kernfs_link_sibling(struct kernfs_node *kn)
rb_insert_color(&kn->rb, &kn->parent->dir.children);

/* successfully added, account subdir number */
+ down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
if (kernfs_type(kn) == KERNFS_DIR)
kn->parent->dir.subdirs++;
kernfs_inc_rev(kn->parent);
+ up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);

return 0;
}
@@ -408,9 +410,11 @@ static bool kernfs_unlink_sibling(struct kernfs_node *kn)
if (RB_EMPTY_NODE(&kn->rb))
return false;

+ down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
if (kernfs_type(kn) == KERNFS_DIR)
kn->parent->dir.subdirs--;
kernfs_inc_rev(kn->parent);
+ up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);

rb_erase(&kn->rb, &kn->parent->dir.children);
RB_CLEAR_NODE(&kn->rb);