linux-kernel - [PATCH] cachefiles: Allow the cache to be non-root

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Date:   Fri, 19 May 2023 18:21:20 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-cachefs@...hat.com
cc:     dhowells@...hat.com, Jeff Layton <jlayton@...nel.org>,
        linux-erofs@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] cachefiles: Allow the cache to be non-root

    
Set mode 0600 on files in the cache so that cachefilesd can run as an
unprivileged user rather than leaving the files all with 0.  Directories
are already set to 0700.

Userspace then needs to set the uid and gid before issuing the "bind"
command and the cache must've been chown'd to those IDs.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: David Howells <dhowells@...hat.com>
cc: Jeff Layton <jlayton@...nel.org>
cc: linux-cachefs@...hat.com
cc: linux-erofs@...ts.ozlabs.org
cc: linux-fsdevel@...r.kernel.org
---
 fs/cachefiles/namei.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
index 82219a8f6084..66482c193e86 100644
--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -451,7 +451,8 @@ struct file *cachefiles_create_tmpfile(struct cachefiles_object *object)
 
 	ret = cachefiles_inject_write_error();
 	if (ret == 0) {
-		file = vfs_tmpfile_open(&nop_mnt_idmap, &parentpath, S_IFREG,
+		file = vfs_tmpfile_open(&nop_mnt_idmap, &parentpath,
+					S_IFREG | 0600,
 					O_RDWR | O_LARGEFILE | O_DIRECT,
 					cache->cache_cred);
 		ret = PTR_ERR_OR_ZERO(file);