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=1793700939; b=gea/f1WNGXUAuCof1QTr7Gt2G6IJI2C+5f8VohD7+1eHqoIDJV7U2L7EfZ4Omq6IiNS6 Y9q4XRheELirBNjBQ2osgetXG+bW5RTldPN+SuozmdusuICoOiE/lSzDw3mrRYWxzHvi9 mOKEYcxQtQdkevqD82qCQ80xA8TUzg7Lql7SHVRut8c14bNBoT3ZeKPDNfEu9EGUXlgFR 2jePdJJcLWjxb0TpG4evjsAfbHTOxn3wo9zpMJQ0KmVG+bYPN3dLoJXsNe9e6t53ajRKm DEp1gkQgykpClljy+9Dci3HlhftB+iPFSdoMzPWlfd+iMczZvFHt+r6490lWPuTnWhw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793700939; h=Received:DKIM-Signature:Subject:To:Cc:From:Date:Message-ID: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=QehXtfYYpPjcWl8YK10telu/czKZvptu0ZQGZAqSA6E=; b=q6T1+PqFGjTzi8R5TBOslus5p7W6RaxUBeKgB/IPfZ2J+XHOyINrh2iJxsYWfNHoQlHO 5nGAqi+dkKrXUGEcprIPG7IoDjJ4V43YBZjYSUGa/p/a9NeIUHQDRIdPl4xd0awN+B5eQ KrfeHTfl2WN3bmgKSvfRZXUHNMCqM7zagdr7dXClphLh2be8MlpuBwhP4iIieXCPqqZoB JxecI7tAxX1tP273hy05M3+mF6hQMpAnLlAvxZSu6SZMGDw9Kmmbs77gitrZjfaIXHrA6 7KIDDUTCPqB4faGbS9F4gPcEy69XtcMSsakVGLFtjRCzs3pGF201ahhvSflkapY/i7w== 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=XT0uodhN; 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 B6241606D80C for ; Tue, 3 Nov 2026 10:15:38 +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=XT0uodhN Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0496D1F000C1; Tue, 3 Nov 2026 10:15:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793700938; bh=QehXtfYYpPjcWl8YK10telu/czKZvptu0ZQGZAqSA6E=; h=Subject:To:Cc:From:Date; b=XT0uodhNtFpbamjnbgpwHNjRQAyAaLG9/WbMBEBDBtXB77V0CanTSiDJoUF+p28MZ M0M8zpETQrB/3H/NYwdTjzd0EFE2okYyzwp+8jLNrYTtDu4OyJohOtwDd1eAGbeT5y kM7FwVkvAJac0vlnwMt8e81mz6jDy4fU3aLjMeIE= Subject: FAILED: patch "[PATCH] ksmbd: deny access for an empty DACL instead of granting the" failed to apply to 6.18-stable tree To: elb12345@hotmail.co.uk,linkinjeon@kernel.org Cc: From: Date: Tue, 03 Nov 2026 11:15:36 +0100 Message-ID: <2026110336-whole-agile-fb2c@gregkh> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y git checkout FETCH_HEAD git cherry-pick -x de0cffef897c1c232ed973f89928cd6c93d0b1e3 # git commit -s git send-email --to '' --in-reply-to '2026110336-whole-agile-fb2c@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From de0cffef897c1c232ed973f89928cd6c93d0b1e3 Mon Sep 17 00:00:00 2001 From: Aamir Ahmed Date: Wed, 16 Sep 2026 11:49:27 +0100 Subject: [PATCH] ksmbd: deny access for an empty DACL instead of granting the request 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 diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c index c959699ace56..664f01263611 100644 --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -1502,21 +1502,27 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path, 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);