linux-kernel - [PATCH] kernfs: fix false-positive WARN(nr_mmapped) in kernfs_drain_open

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date: Sat, 27 Jan 2024 15:46:36 -0800
From: Neel Natu <neelnatu@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Tejun Heo <tj@...nel.org>
Cc: linux-kernel@...r.kernel.org, Neel Natu <neelnatu@...gle.com>
Subject: [PATCH] kernfs: fix false-positive WARN(nr_mmapped) in kernfs_drain_open_files

Prior to this change 'on->nr_mmapped' tracked the total number of
mmaps across all of its associated open files via kernfs_fop_mmap().
Thus if the file descriptor associated with a kernfs_open_file was
mmapped 10 times then we would have: 'of->mmapped = true' and
'of_on(of)->nr_mmapped = 10'.

The problem is that closing or draining a 'of->mmapped' file would
only decrement one from the 'of_on(of)->nr_mmapped' counter.

For e.g. we have this from kernfs_unlink_open_file():
        if (of->mmapped)
                on->nr_mmapped--;

The WARN_ON_ONCE(on->nr_mmapped) in kernfs_drain_open_files() is
easy to reproduce by:
1. opening a (mmap-able) kernfs file.
2. mmap-ing that file more than once (mapping just once masks the issue).
3. trigger a drain of that kernfs file.

Modulo out-of-tree patches I was able to trigger this reliably by
identifying pci device nodes in sysfs that have resource regions
that are mmap-able and that don't have any driver attached to them
(steps 1 and 2). For step 3 we can "echo 1 > remove" to trigger a
kernfs_drain.

Signed-off-by: Neel Natu <neelnatu@...gle.com>
---
 fs/kernfs/file.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index ffa4565c275a..e9df2f87072c 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -483,9 +483,11 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
 		goto out_put;

 	rc = 0;
-	of->mmapped = true;
-	of_on(of)->nr_mmapped++;
-	of->vm_ops = vma->vm_ops;
+	if (!of->mmapped) {
+		of->mmapped = true;
+		of_on(of)->nr_mmapped++;
+		of->vm_ops = vma->vm_ops;
+	}
 	vma->vm_ops = &kernfs_vm_ops;
 out_put:
 	kernfs_put_active(of->kn);
-- 
2.43.0.429.g432eaa2c6b-goog