linux-kernel - [PATCH] vfs: bypass may_create_in_sticky check if task has CAP

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:   Wed, 27 Jul 2022 08:30:48 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     viro@...iv.linux.org.uk
Cc:     linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, Yongchen Yang <yoyang@...hat.com>,
        Christian Brauner <brauner@...nel.org>
Subject: [PATCH] vfs: bypass may_create_in_sticky check if task has CAP_FOWNER

NFS server is exporting a sticky directory (mode 01777) with root
squashing enabled. Client has protect_regular enabled and then tries to
open a file as root in that directory. File is created (with ownership
set to nobody:nobody) but the open syscall returns an error.

The problem is may_create_in_sticky, which rejects the open even though
the file has already been created/opened. Bypass the checks in
may_create_in_sticky if the task has CAP_FOWNER in the given namespace.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829
Reported-by: Yongchen Yang <yoyang@...hat.com>
Suggested-by: Christian Brauner <brauner@...nel.org>
Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 fs/namei.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 1f28d3f463c3..170c2396ba29 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1230,7 +1230,8 @@ static int may_create_in_sticky(struct user_namespace *mnt_userns,
 	    (!sysctl_protected_regular && S_ISREG(inode->i_mode)) ||
 	    likely(!(dir_mode & S_ISVTX)) ||
 	    uid_eq(i_uid_into_mnt(mnt_userns, inode), dir_uid) ||
-	    uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)))
+	    uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) ||
+	    ns_capable(mnt_userns, CAP_FOWNER))
 		return 0;
 
 	if (likely(dir_mode & 0002) ||
-- 
2.37.1