kernfs: fix ino wrap-around detection

When the 32bit ino wraps around, kernfs increments the generation
number to distinguish reused ino instances.  The wrap-around detection
tests whether the allocated ino is lower than what the cursor but the
cursor is pointing to the next ino to allocate so the condition never
triggers.

Fix it by remembering the last ino and comparing against that.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Fixes: 4a3ef68acacf ("kernfs: implement i_generation")
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: stable@vger.kernel.org # v4.14+

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 6ebae6bbe6a5e6f127aab0318f3d06045bed837e..7d4af6cea2a63f5253d7c4216e1b8db7387c4801 100644 (file)
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -622,7 +622,6 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
 {
        struct kernfs_node *kn;
        u32 gen;
-       int cursor;
        int ret;
 
        name = kstrdup_const(name, GFP_KERNEL);
@@ -635,11 +634,11 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
 
        idr_preload(GFP_KERNEL);
        spin_lock(&kernfs_idr_lock);
-       cursor = idr_get_cursor(&root->ino_idr);
        ret = idr_alloc_cyclic(&root->ino_idr, kn, 1, 0, GFP_ATOMIC);
-       if (ret >= 0 && ret < cursor)
+       if (ret >= 0 && ret < root->last_ino)
                root->next_generation++;
        gen = root->next_generation;
+       root->last_ino = ret;
        spin_unlock(&kernfs_idr_lock);
        idr_preload_end();
        if (ret < 0)

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 936b61bd504e45848444ae67bc218466379e8b7a..f797ccc650e798d61802af9c3a2db3179c346254 100644 (file)
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -187,6 +187,7 @@ struct kernfs_root {
 
        /* private fields, do not use outside kernfs proper */
        struct idr              ino_idr;
+       u32                     last_ino;
        u32                     next_generation;
        struct kernfs_syscall_ops *syscall_ops;