linux-kernel - [PATCH AUTOSEL 5.16 20/30] cifs: modefromsids must add an ACE for authenticated users

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Date:   Tue, 22 Feb 2022 21:28:09 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Ronnie Sahlberg <lsahlber@...hat.com>,
        Shyam Prasad N <sprasad@...rosoft.com>,
        Steve French <stfrench@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>, sfrench@...ba.org,
        linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org
Subject: [PATCH AUTOSEL 5.16 20/30] cifs: modefromsids must add an ACE for authenticated users

From: Ronnie Sahlberg <lsahlber@...hat.com>

[ Upstream commit 0c6f4ebf8835d01866eb686d47578cde80097981 ]

When we create a file with modefromsids we set an ACL that
has one ACE for the magic modefromsid as well as a second ACE that
grants full access to all authenticated users.

When later we chante the mode on the file we strip away this, and other,
ACE for authenticated users in set_chmod_dacl() and then just add back/update
the modefromsid ACE.
Thus leaving the file with a single ACE that is for the mode and no ACE
to grant any user any rights to access the file.
Fix this by always adding back also the modefromsid ACE so that we do not
drop the rights to access the file.

Signed-off-by: Ronnie Sahlberg <lsahlber@...hat.com>
Reviewed-by: Shyam Prasad N <sprasad@...rosoft.com>
Signed-off-by: Steve French <stfrench@...rosoft.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/cifs/cifsacl.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c
index 5df21d63dd04e..bf861fef2f0c3 100644
--- a/fs/cifs/cifsacl.c
+++ b/fs/cifs/cifsacl.c
@@ -949,6 +949,9 @@ static void populate_new_aces(char *nacl_base,
 		pnntace = (struct cifs_ace *) (nacl_base + nsize);
 		nsize += setup_special_mode_ACE(pnntace, nmode);
 		num_aces++;
+		pnntace = (struct cifs_ace *) (nacl_base + nsize);
+		nsize += setup_authusers_ACE(pnntace);
+		num_aces++;
 		goto set_size;
 	}
 
@@ -1613,7 +1616,7 @@ id_mode_to_cifs_acl(struct inode *inode, const char *path, __u64 *pnmode,
 	nsecdesclen = secdesclen;
 	if (pnmode && *pnmode != NO_CHANGE_64) { /* chmod */
 		if (mode_from_sid)
-			nsecdesclen += sizeof(struct cifs_ace);
+			nsecdesclen += 2 * sizeof(struct cifs_ace);
 		else /* cifsacl */
 			nsecdesclen += 5 * sizeof(struct cifs_ace);
 	} else { /* chown */
-- 
2.34.1