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kernfs: fix ino wrap-around detection

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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: 4a3ef68aca ("kernfs: implement i_generation")
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: stable@vger.kernel.org # v4.14+
This commit is contained in:
Tejun Heo 2019-11-04 15:54:29 -08:00
parent d671fa6393
commit e23f568aa6
2 changed files with 3 additions and 3 deletions
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5
fs/kernfs/dir.c
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@ -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)

1
include/linux/kernfs.h
View File

@ -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;