From: Christian Brauner <brauner@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jann Horn <jannh@google.com>, Jan Kara <jack@suse.cz>,
Amir Goldstein <amir73il@gmail.com>,
linux-fsdevel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
"Christian Brauner (Amutable)" <brauner@kernel.org>
Subject: [PATCH RFC v2 1/8] fs: refuse fspick() on internal superblocks
Date: Fri, 25 Sep 2026 00:35:41 +0200 [thread overview]
Message-ID: <20260925-work-mount-knullfs-v2-1-c4aebaa186e9@kernel.org> (raw)
In-Reply-To: <20260925-work-mount-knullfs-v2-0-c4aebaa186e9@kernel.org>
There's a few instances where a internal superblock is reachable by
fspick(). Block that. graft_tree() and fsmount() already refuse them.
fanotify refuses mount and superblock marks on them for the same reason.
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
fs/fsopen.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/fs/fsopen.c b/fs/fsopen.c
index ae19e5136598..9d5a7a22b529 100644
--- a/fs/fsopen.c
+++ b/fs/fsopen.c
@@ -190,6 +190,9 @@ SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags
ret = -EINVAL;
if (target.mnt->mnt_root != target.dentry)
goto err_path;
+ /* kernel-internal superblocks are nobody's to reconfigure */
+ if (target.dentry->d_sb->s_flags & SB_NOUSER)
+ goto err_path;
fc = fs_context_for_reconfigure(target.dentry, 0, 0);
if (IS_ERR(fc)) {
--
2.53.0
next prev parent reply other threads:[~2026-09-24 22:35 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-24 22:35 [PATCH RFC v2 0/8] namespace: prevent UMOUNT_CONNECTED reference count cycles Christian Brauner
2026-09-24 22:35 ` Christian Brauner [this message]
2026-09-24 22:35 ` [PATCH RFC v2 2/8] fsnotify: record the superblock a connector is accounted on Christian Brauner
2026-09-24 22:35 ` [PATCH RFC v2 3/8] fs: put the old fs_struct before the old namespaces in unshare() Christian Brauner
2026-09-24 22:35 ` [PATCH RFC v2 4/8] namespace: drop the file's reference first in dissolve_on_fput() Christian Brauner
2026-09-24 22:35 ` [PATCH RFC v2 5/8] namespace: prevent UMOUNT_CONNECTED reference count cycles Christian Brauner
2026-09-24 22:35 ` [PATCH RFC v2 6/8] selftests/filesystems: check that a loop mount below a dead mount is released Christian Brauner
2026-09-24 22:35 ` [PATCH RFC v2 7/8] selftests/filesystems: check the two-step cycle over crossed loop images Christian Brauner
2026-09-24 22:35 ` [PATCH RFC v2 8/8] selftests/filesystems: check that the holders let go of a dead mount Christian Brauner
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