linux-kernel - [PATCH] fs: Delete group check before ACL

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Date:   Thu, 10 Nov 2022 20:37:44 +0800
From:   Wang Boshi <wangboshi@...wei.com>
To:     <viro@...iv.linux.org.uk>
CC:     <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] fs: Delete group check before ACL

Skipping full file ACL checks without no Group permissions causes we
can't deny access from specific users or groups which we ban according
ACL_USER, ACL_GROUP and ACL_MASK rules, because they may pass due to
Other permissions.

Example:
  date > test_file
  setfacl -m u:1000:rwx,g:2000:rwx,u::rwx,g::rwx,o::rwx,m::0 test_file
  capsh --groups=1000 --gid=1000 --uid=1000 -- -c "cat test_file"
  capsh --groups=2000 --gid=2000 --uid=2000 -- -c "cat test_file"

Signed-off-by: Wang Boshi <wangboshi@...wei.com>
---
 fs/namei.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 578c2110df02..d5772a31b5fc 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -347,7 +347,7 @@ static int acl_permission_check(struct user_namespace *mnt_userns,
 	}
 
 	/* Do we have ACL's? */
-	if (IS_POSIXACL(inode) && (mode & S_IRWXG)) {
+	if (IS_POSIXACL(inode)) {
 		int error = check_acl(mnt_userns, inode, mask);
 		if (error != -EAGAIN)
 			return error;
-- 
2.29.2