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Date: Tue, 16 Jun 2020 17:33:56 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Avi Kivity <avi@...lladb.com>, Giuseppe Scrivano <gscrivan@...hat.com>, Miklos Szeredi <mszeredi@...hat.com>, Christoph Hellwig <hch@....de> Subject: [PATCH 5.6 046/161] aio: fix async fsync creds From: Miklos Szeredi <mszeredi@...hat.com> commit 530f32fc370fd1431ea9802dbc53ab5601dfccdb upstream. Avi Kivity reports that on fuse filesystems running in a user namespace asyncronous fsync fails with EOVERFLOW. The reason is that f_ops->fsync() is called with the creds of the kthread performing aio work instead of the creds of the process originally submitting IOCB_CMD_FSYNC. Fuse sends the creds of the caller in the request header and it needs to translate the uid and gid into the server's user namespace. Since the kthread is running in init_user_ns, the translation will fail and the operation returns an error. It can be argued that fsync doesn't actually need any creds, but just zeroing out those fields in the header (as with requests that currently don't take creds) is a backward compatibility risk. Instead of working around this issue in fuse, solve the core of the problem by calling the filesystem with the proper creds. Reported-by: Avi Kivity <avi@...lladb.com> Tested-by: Giuseppe Scrivano <gscrivan@...hat.com> Fixes: c9582eb0ff7d ("fuse: Fail all requests with invalid uids or gids") Cc: stable@...r.kernel.org # 4.18+ Signed-off-by: Miklos Szeredi <mszeredi@...hat.com> Reviewed-by: Christoph Hellwig <hch@....de> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- fs/aio.c | 8 ++++++++ 1 file changed, 8 insertions(+) --- a/fs/aio.c +++ b/fs/aio.c @@ -176,6 +176,7 @@ struct fsync_iocb { struct file *file; struct work_struct work; bool datasync; + struct cred *creds; }; struct poll_iocb { @@ -1589,8 +1590,11 @@ static int aio_write(struct kiocb *req, static void aio_fsync_work(struct work_struct *work) { struct aio_kiocb *iocb = container_of(work, struct aio_kiocb, fsync.work); + const struct cred *old_cred = override_creds(iocb->fsync.creds); iocb->ki_res.res = vfs_fsync(iocb->fsync.file, iocb->fsync.datasync); + revert_creds(old_cred); + put_cred(iocb->fsync.creds); iocb_put(iocb); } @@ -1604,6 +1608,10 @@ static int aio_fsync(struct fsync_iocb * if (unlikely(!req->file->f_op->fsync)) return -EINVAL; + req->creds = prepare_creds(); + if (!req->creds) + return -ENOMEM; + req->datasync = datasync; INIT_WORK(&req->work, aio_fsync_work); schedule_work(&req->work);
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