From 0618021e34c6b1edc4fc754ec53ab7fdcc98aaec Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 14 Sep 2022 16:26:32 +0200 Subject: fuse: Remove user_ns check for FUSE_DEV_IOC_CLONE Commit 8ed1f0e22f49e ("fs/fuse: fix ioctl type confusion") fixed a type confusion bug by adding an ->f_op comparison. Based on some off-list discussion back then, another check was added to compare the f_cred->user_ns. This is not for security reasons, but was based on the idea that a FUSE device FD should be using the UID/GID mappings of its f_cred->user_ns, and those translations are done using fc->user_ns, which matches the f_cred->user_ns of the initial FUSE device FD thanks to the check in fuse_fill_super(). See also commit 8cb08329b0809 ("fuse: Support fuse filesystems outside of init_user_ns"). But FUSE_DEV_IOC_CLONE is, at a higher level, a *cloning* operation that copies an existing context (with a weird API that involves first opening /dev/fuse, then tying the resulting new FUSE device FD to an existing FUSE instance). So if an application is already passing FUSE FDs across userns boundaries and dealing with the resulting ID mapping complications somehow, it doesn't make much sense to block this cloning operation. I've heard that this check is an obstacle for some folks, and I don't see a good reason to keep it, so remove it. Signed-off-by: Jann Horn Signed-off-by: Miklos Szeredi --- fs/fuse/dev.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'fs/fuse') diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 0a845fac3ba8..c73d9c4132f6 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -2267,8 +2267,7 @@ static long fuse_dev_ioctl(struct file *file, unsigned int cmd, * Check against file->f_op because CUSE * uses the same ioctl handler. */ - if (old->f_op == file->f_op && - old->f_cred->user_ns == file->f_cred->user_ns) + if (old->f_op == file->f_op) fud = fuse_get_dev(old); if (fud) { -- cgit v1.2.3