From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793826971; b=TspndmeKpmtok7Wbbzd1GsZaa5S2wYk+iVHe+4KWkvdJ3Nt2M58hrLRMwWoHMjCXYeDp BCC5+nJVVnT7BLIqq96h1Wr+YgJm6bdbZBtAWSqkBUhdcfsRiWCg1gu6EoGlC4OzIDoVZ mLgNnsuIzAkWUDOSbZClnwdWXSPJznqCjQnTfH24JnFrBiXkJOHg6MYYcp15SIvA0U536 siyKGkr4We4CICATLJyw8SEpRNKxHEWAfuepfirstko4Mc7BOWTCtLDZ6Ak1KMCXEceGH bQi4mXPX3av0mrDvObYC6WnFjaDNkYhV7wywlOQxSFCnzjCRgXfPwLbLo6ZkTi48peA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793826971; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=/n3yWd+mDpcqwxaKusSa3Yn+AzgIszIfLEDXJLQmCiA=; b=ln5/dgRoNQ59i1sm5XgvEWzRMuC6CdwCu7OoLUueqZOkwn34Qu0MaIAA52lBdCPxvEEH ZJ7fU+ldPZPOueaUVBmDBOWoRrosbs/AZkZ84Q/t+veCofHjIybPare05H2gZGyEK9SZz rLcsVcv8NPA66ugygLTVqUxa4TeLJvZidppz7v8xrSa7iAGgy+rE44NdxsQeLhBtubbwM /kL+19toqEWUsV7p2mPArA2SWAuPGpKBPojmE7zeWcG3jI56lG1ktvYxMtmiWSn7B8dQQ h5GSperHsL+Zwc5kFq3FBHpu4DMxHFsHwu5Lpnt/iVef/z0JWNUis3EZ/0S4+6MjcFQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=Ha+lVpA3; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C77836070336; Wed, 4 Nov 2026 21:16:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=Ha+lVpA3 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1FBA61F00A18; Wed, 4 Nov 2026 21:16:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793826970; bh=/n3yWd+mDpcqwxaKusSa3Yn+AzgIszIfLEDXJLQmCiA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Ha+lVpA3jKh4hNqE26SounsA4TxsT0JemVbBsK6H0mheP52O0pZUjmQH097n4rD30 ZKU2th3CXTE/GnrxcWlrKqajED6MW7+ZJmYZkynkMqhsmo4Dp60NWk5jliqiu0+b6c BCYvpuJZNYc67FxnGUvMQJ5VATnIFzR1q2kp9g0o= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Aamir Ahmed , Namjae Jeon Subject: [PATCH 7.3 116/547] ksmbd: deny access for an empty DACL instead of granting the request Date: Wed, 4 Nov 2026 16:05:00 -0500 Message-ID: <20261104211041.498019132@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261104211038.406938024@linuxfoundation.org> References: <20261104211038.406938024@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Aamir Ahmed commit de0cffef897c1c232ed973f89928cd6c93d0b1e3 upstream. smb_check_perm_dacl() returns the access mask it computes to the SMB2 CREATE handler, which uses it as the granted access for the open. For a security descriptor whose DACL is present but contains no ACEs, the function is supposed to deny access: an empty (non-NULL) DACL grants no access to anyone except the object owner's implicit READ_CONTROL and WRITE_DAC (MS-DTYP 2.4.5). The empty-DACL branch only denies when both - the DACL has no trailing bytes (pdacl_size == sizeof(struct smb_acl)), and - the request contains bits beyond READ_CONTROL / WRITE_DAC. In every other case it takes the shared "goto err_out" with rc still 0, which returns success without modifying *pdaccess, so the caller grants the full requested access. Three problems follow: - The READ_CONTROL / WRITE_DAC carve-out models the owner's implicit rights, but the check runs before is_owner is computed, so those rights are handed to *every* caller, not just the owner. For READ_CONTROL the SMB2 CREATE path does not fall back to inode_permission(), so any user can read the security descriptor of an object whose empty DACL is meant to deny them. - A request of exactly READ_CONTROL and/or WRITE_DAC is granted to any caller. WRITE_DAC lets the handle rewrite the DACL. - A DACL that declares zero ACEs but carries trailing bytes (pdacl_size > sizeof(struct smb_acl)) skips the deny entirely and is granted whatever was requested. On shares where the NT ACL is the authoritative access control -- e.g. "force user" shares, where every client maps to one POSIX identity so POSIX cannot distinguish users -- this is an access-control bypass. Compute is_owner before the empty-DACL branch and deny access from an empty DACL unless the caller is the owner requesting no more than READ_CONTROL / WRITE_DAC. Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Aamir Ahmed Signed-off-by: Namjae Jeon Signed-off-by: Greg Kroah-Hartman --- fs/smb/server/smbacl.c | 24 +++++++++++++++--------- 1 file changed, 15 insertions(+), 9 deletions(-) --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -1490,21 +1490,27 @@ int smb_check_perm_dacl(struct ksmbd_con if (pdacl_size > acl_size || pdacl_size < sizeof(struct smb_acl)) goto err_out; - if (!pdacl->num_aces) { - if (!(pdacl_size - sizeof(struct smb_acl)) && - *pdaccess & ~(FILE_READ_CONTROL_LE | FILE_WRITE_DAC_LE)) { - rc = -EACCES; - goto err_out; - } - goto err_out; - } - if (!uid) sid_type = SIDUNIX_USER; id_to_sid(uid, sid_type, &sid); vfsuid = i_uid_into_vfsuid(idmap, d_inode(path->dentry)); is_owner = uid == from_kuid(&init_user_ns, vfsuid_into_kuid(vfsuid)); + if (!pdacl->num_aces) { + /* + * An empty (present, zero-ACE) DACL grants no access to + * anyone except the object owner's implicit READ_CONTROL + * and WRITE_DAC (MS-DTYP 2.4.5). Deny every other caller, + * deny the owner any access beyond those two bits, and do + * not let trailing bytes after a zero-ACE DACL become an + * implicit grant. + */ + if (!is_owner || + (*pdaccess & ~(FILE_READ_CONTROL_LE | FILE_WRITE_DAC_LE))) + rc = -EACCES; + goto err_out; + } + if (*pdaccess & FILE_MAXIMAL_ACCESS_LE) { ace = (struct smb_ace *)((char *)pdacl + sizeof(struct smb_acl)); aces_size = pdacl_size - sizeof(struct smb_acl);