linux-kernel - [PATCH] fs/posix_acl: apply umask if superblock disables ACL support

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Message-Id: <20230919081808.1096542-1-max.kellermann@ionos.com>
Date:   Tue, 19 Sep 2023 10:18:07 +0200
From:   Max Kellermann <max.kellermann@...os.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>
Cc:     Max Kellermann <max.kellermann@...os.com>,
        "J . Bruce Fields" <bfields@...hat.com>, stable@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] fs/posix_acl: apply umask if superblock disables ACL support

The function posix_acl_create() applies the umask only if the inode
has no ACL (= NULL) or if ACLs are not supported by the filesystem
driver (= -EOPNOTSUPP).

However, this happens only after after the IS_POSIXACL() check
succeeded.  If the superblock doesn't enable ACL support, umask will
never be applied.  A filesystem which has no ACL support will of
course not enable SB_POSIXACL, rendering the umask-applying code path
unreachable.

This fixes a bug which causes the umask to be ignored with O_TMPFILE
on tmpfs:

 https://github.com/MusicPlayerDaemon/MPD/issues/558
 https://bugs.gentoo.org/show_bug.cgi?id=686142#c3
 https://bugzilla.kernel.org/show_bug.cgi?id=203625

Reviewed-by: J. Bruce Fields <bfields@...hat.com>
Cc: stable@...r.kernel.org
Signed-off-by: Max Kellermann <max.kellermann@...os.com>
---
 fs/posix_acl.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index a05fe94970ce..79831269dd2f 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -642,9 +642,14 @@ posix_acl_create(struct inode *dir, umode_t *mode,
 	*acl = NULL;
 	*default_acl = NULL;
 
-	if (S_ISLNK(*mode) || !IS_POSIXACL(dir))
+	if (S_ISLNK(*mode))
 		return 0;
 
+	if (!IS_POSIXACL(dir)) {
+		*mode &= ~current_umask();
+		return 0;
+	}
+
 	p = get_inode_acl(dir, ACL_TYPE_DEFAULT);
 	if (!p || p == ERR_PTR(-EOPNOTSUPP)) {
 		*mode &= ~current_umask();
-- 
2.39.2