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=1793720056; b=Xcqoe5UZPsVqwNZCsUhgrJIswtrMOueZaM5VlOtw3AHZp6IjUg6/j9fzmppE03rnMed5 Vvqafg9QESEiVXiK1QJikodyPTJNis0uYUkaTNl7qLSVlGsar4Vxri6OcfG2l97GI4n4x AGCYcAt4S2tAnwricQNSEeNUEvZ2Cnt1yF6sQSqQwLjSgliNCpoD9Sys/4CgM1/g9L6pa eDZ2WA1KPtCFFNHZf38txEd2gLuO1ZgnbN9uYAGwMixZYWAOdhlZqIvaNwI3sh9HIzsxY BHMt7eWeYgWzDOxjB8YPfBjeL7EXVqVcRKCsIhVTfdeUf5pStO1LIL8jWOKnQlXJyXA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793720056; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=7cas561+VSJ9fHR+gCNDM4Q2PPKbIkxfUd4h6ZbzNXI=; b=BEH2U/4qFRCHzcc8nTXghFkTYk+EhyYHbrE59PQiRldjkHOUiMrYf88cSUP4+kd0sA+i fYaxvqDW0Zwr9y5vAoO3RH1NhPOiHRbdww/XL7/kT11Yqdv4GtdRm3nn6J7TJq2yRexxM H/AmaSYWQE6o3oQ9Dzx4MPpkvNLvtlXO4S60n16QAAjNbv/ur7JDcA7Yg7Lc/u3n5UjA4 W3XgT7Jxb7Fxaolt5qV1z8VHcYJCtvl76NjpHKvjHB0PN18a/nEoKPdZCqT8YbnvGQrkh Xgrf9YX6YIXXCu7PoozPdqGar/dtuF+/XDeBIEistt/35Z46pozpnSv1GhwLsjhKk7Q== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cAMh8Pjw; 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 5069E606A324 for ; Tue, 3 Nov 2026 15:34:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cAMh8Pjw Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7D61B1F000C1; Tue, 3 Nov 2026 15:34:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793720056; bh=7cas561+VSJ9fHR+gCNDM4Q2PPKbIkxfUd4h6ZbzNXI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=cAMh8PjwMpIeUVkyhACsO/9CtpAE5DUGFCmhs5V7d4pbhYzcEC+yGtuAFQBtxSf1V nYO0d3T1v9PsWe43+gN5J8duIvxweTzHBRWZ9TvqX8P8JwrmACTQK8AneOV7eutUPX wjiHClHFgZxS+cwGiMi1xGqInCCs1iyZMSoDItVJEqFjTZ+p9dY9p3KEj6zZ2CcS0X EmwlLEyng5UhcsTp294N+QmoL8Bb6Ui9EGvxCmPwAnzI2EiLEfLIsSF51qCJuDsfMV 1UenF9bHfCjrIFvqHZb9bUp7bXoMWC0JbDp+FB/9T6ITdW66+YXFG1SdjK6l+UAQjr lZg+JsbTYxjjQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Aamir Ahmed , Namjae Jeon , Sasha Levin Subject: [PATCH 6.12.y] ksmbd: deny access for an empty DACL instead of granting the request Date: Tue, 3 Nov 2026 10:34:14 -0500 Message-ID: <20261103153341.254176-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026110337-headed-quirk-3494@gregkh> References: <2026110337-headed-quirk-3494@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-Transfer-Encoding: 8bit From: Aamir Ahmed [ Upstream commit de0cffef897c1c232ed973f89928cd6c93d0b1e3 ] 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 [ sashal: added the missing mount-mapped UID ownership calculation for is_owner ] Signed-off-by: Sasha Levin --- fs/smb/server/smbacl.c | 26 ++++++++++++++++++-------- 1 file changed, 18 insertions(+), 8 deletions(-) diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c index 49a35974dd296..33a607e709f18 100644 --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -1469,6 +1469,8 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path, struct posix_acl_entry *pa_entry; unsigned int sid_type = SIDOWNER; unsigned short ace_size; + bool is_owner; + vfsuid_t vfsuid; ksmbd_debug(SMB, "check permission using windows acl\n"); pntsd_size = ksmbd_vfs_get_sd_xattr(conn, idmap, @@ -1489,19 +1491,27 @@ 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 (!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) { - if (!(pdacl_size - sizeof(struct smb_acl)) && - *pdaccess & ~(FILE_READ_CONTROL_LE | FILE_WRITE_DAC_LE)) { + /* + * 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; - } goto err_out; } - if (!uid) - sid_type = SIDUNIX_USER; - id_to_sid(uid, sid_type, &sid); - if (*pdaccess & FILE_MAXIMAL_ACCESS_LE) { access_bits = READ_CONTROL | WRITE_DAC | FILE_READ_ATTRIBUTES | DELETE; -- 2.53.0