[PATCH] cachefiles: fix incorrect dentry refcount in cachefiles_cull()

[PATCH] cachefiles: fix incorrect dentry refcount in cachefiles_cull()

[NeilBrown]

The patch mentioned below changed cachefiles_bury_object() to expect 2
references to the 'rep' dentry.  Three of the callers were changed to
use start_removing_dentry() which takes an extra reference so in those
cases the call gets the expected references.

However there is another call to cachefiles_bury_object() in
cachefiles_cull() which did not need to be changed to use
start_removing_dentry() and so was not properly considered.
It still passed the dentry with just one reference so the net result is
that a reference is lost.

To meet the expectations of cachefiles_bury_object(), cachefiles_cull()
must take an extra reference before the call.  It will be dropped by
cachefiles_bury_object().

Reported-by: Marc Dionne <marc.dionne@auristor.com>
Fixes: 7bb1eb45e43c ("VFS: introduce start_removing_dentry()")
Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/cachefiles/namei.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
index b498c210112b..1b83ed0e0a63 100644
--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -781,6 +781,11 @@ int cachefiles_cull(struct cachefiles_cache *cache, struct dentry *dir,
 	if (ret < 0)
 		goto error_unlock;
 
+	/*
+	 * cachefiles_bury_object() expects 2 references to 'victim',
+	 * and drops one.
+	 */
+	dget(victim);
 	ret = cachefiles_bury_object(cache, NULL, dir, victim,
 				     FSCACHE_OBJECT_WAS_CULLED);
 	dput(victim);

base-commit: 84f524dca4b8bc9e9aca8ea1dbbd2aa3a239d998
-- 
2.50.0.107.gf914562f5916.dirty

Re: [PATCH] cachefiles: fix incorrect dentry refcount in cachefiles_cull()

[Paulo Alcantara]

NeilBrown <neilb@ownmail.net> writes:

> The patch mentioned below changed cachefiles_bury_object() to expect 2
> references to the 'rep' dentry.  Three of the callers were changed to
> use start_removing_dentry() which takes an extra reference so in those
> cases the call gets the expected references.
>
> However there is another call to cachefiles_bury_object() in
> cachefiles_cull() which did not need to be changed to use
> start_removing_dentry() and so was not properly considered.
> It still passed the dentry with just one reference so the net result is
> that a reference is lost.
>
> To meet the expectations of cachefiles_bury_object(), cachefiles_cull()
> must take an extra reference before the call.  It will be dropped by
> cachefiles_bury_object().
>
> Reported-by: Marc Dionne <marc.dionne@auristor.com>
> Fixes: 7bb1eb45e43c ("VFS: introduce start_removing_dentry()")
> Signed-off-by: NeilBrown <neil@brown.name>
> ---
>  fs/cachefiles/namei.c | 5 +++++
>  1 file changed, 5 insertions(+)

Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>

Re: [PATCH] cachefiles: fix incorrect dentry refcount in cachefiles_cull()

[Christian Brauner]

On Fri, 27 Mar 2026 09:18:21 +1100, NeilBrown wrote:
> The patch mentioned below changed cachefiles_bury_object() to expect 2
> references to the 'rep' dentry.  Three of the callers were changed to
> use start_removing_dentry() which takes an extra reference so in those
> cases the call gets the expected references.
> 
> However there is another call to cachefiles_bury_object() in
> cachefiles_cull() which did not need to be changed to use
> start_removing_dentry() and so was not properly considered.
> It still passed the dentry with just one reference so the net result is
> that a reference is lost.
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] cachefiles: fix incorrect dentry refcount in cachefiles_cull()
      https://git.kernel.org/vfs/vfs/c/1635c2acdde8