From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F161C19D89E for ; Fri, 24 Apr 2026 17:25:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777051515; cv=none; b=E+ju6bLbqYQobBm7X0oZCdXyBGwNt/175l9Jnhanw4rPQTGDpgT5gLPWHCP4yI65/TIRbd6ZxNNtd8hvopxQidzBSAgbWXqkB92XqgLHC6hkVSdlVMn5fu1NPRNzQ6pla6KBDglOlKi7/6knRinSVV3czhGHrScBo9VPWACpvAM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777051515; c=relaxed/simple; bh=dMLA+2B0tNgwHHRcPOX3qA7yR+LVQuj7tajUVpjDaBc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Y1eUlNjeqfecdKXs941Cdr89dnrc+L5490Gr4IJFMHZY0ireUV946sr2ZK2NMZQ44BAqZvhmZ3XslC+xoypbRxvWW2FvmX/Fgrz2aSRz0M4/lLzq2U8qcQz2rp2Oa9jU1TIwt2kFxPtrYtvPzh//Xvbs6D+unI7nnC07dE3xGhI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VHM3bIyy; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VHM3bIyy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 47F15C19425; Fri, 24 Apr 2026 17:25:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777051514; bh=dMLA+2B0tNgwHHRcPOX3qA7yR+LVQuj7tajUVpjDaBc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VHM3bIyyKdZRUAywb5n6y+ZTvvUXOh5opmtBB7+dicCK3gCaf2ekbDVMC4cK1S8Ue PEhgdaMXC0z5hYWaaOu9TfBfgwDDul0xkc9LX74/riYThSUCGfkRhxfxBhWXju7oTv Yxc6+iJYKtl6ZgyagAKvkRlsHPzw9awOA105ehu/gTmwUOGFopyvHvFa/QqtPMQ/UB +O/bjY4pMU6Q5VSjUrionAgvtEmTy24V3Qi8JA2hA4DAlQVbxHvlOa3ILJGl+3Qzkt q6gjLZFg5z1nexHZSKznUkRFtNj/R7uQ5UheJDUJxTCNjjkFuNYudMs9wRaGHxijD/ LGouKSWdy52BA== From: Sasha Levin To: stable@vger.kernel.org Cc: Michael Bommarito , Namjae Jeon , Steve French , Sasha Levin Subject: [PATCH 5.15.y] ksmbd: require minimum ACE size in smb_check_perm_dacl() Date: Fri, 24 Apr 2026 13:25:12 -0400 Message-ID: <20260424172512.2372287-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026042429-think-provoking-8c8b@gregkh> References: <2026042429-think-provoking-8c8b@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Michael Bommarito [ Upstream commit d07b26f39246a82399661936dd0c853983cfade7 ] Both ACE-walk loops in smb_check_perm_dacl() only guard against an under-sized remaining buffer, not against an ACE whose declared `ace->size` is smaller than the struct it claims to describe: if (offsetof(struct smb_ace, access_req) > aces_size) break; ace_size = le16_to_cpu(ace->size); if (ace_size > aces_size) break; The first check only requires the 4-byte ACE header to be in bounds; it does not require access_req (4 bytes at offset 4) to be readable. An attacker who has set a crafted DACL on a file they own can declare ace->size == 4 with aces_size == 4, pass both checks, and then granted |= le32_to_cpu(ace->access_req); /* upper loop */ compare_sids(&sid, &ace->sid); /* lower loop */ reads access_req at offset 4 (OOB by up to 4 bytes) and ace->sid at offset 8 (OOB by up to CIFS_SID_BASE_SIZE + SID_MAX_SUB_AUTHORITIES * 4 bytes). Tighten both loops to require ace_size >= offsetof(struct smb_ace, sid) + CIFS_SID_BASE_SIZE which is the smallest valid on-wire ACE layout (4-byte header + 4-byte access_req + 8-byte sid base with zero sub-auths). Also reject ACEs whose sid.num_subauth exceeds SID_MAX_SUB_AUTHORITIES before letting compare_sids() dereference sub_auth[] entries. parse_sec_desc() already enforces an equivalent check (lines 441-448); smb_check_perm_dacl() simply grew weaker validation over time. Reachability: authenticated SMB client with permission to set an ACL on a file. On a subsequent CREATE against that file, the kernel walks the stored DACL via smb_check_perm_dacl() and triggers the OOB read. Not pre-auth, and the OOB read is not reflected to the attacker, but KASAN reports and kernel state corruption are possible. Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-6 Assisted-by: Codex:gpt-5-4 Signed-off-by: Michael Bommarito Acked-by: Namjae Jeon Signed-off-by: Steve French [ changed le16_to_cpu to le32_to_cpu for num_aces field which is __le32 ] Signed-off-by: Sasha Levin --- fs/ksmbd/smbacl.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/fs/ksmbd/smbacl.c b/fs/ksmbd/smbacl.c index ecf9db3d69c38..8d0e1b1c3cdc6 100644 --- a/fs/ksmbd/smbacl.c +++ b/fs/ksmbd/smbacl.c @@ -1265,10 +1265,13 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path, ace = (struct smb_ace *)((char *)pdacl + sizeof(struct smb_acl)); aces_size = acl_size - sizeof(struct smb_acl); for (i = 0; i < le32_to_cpu(pdacl->num_aces); i++) { - if (offsetof(struct smb_ace, access_req) > aces_size) + if (offsetof(struct smb_ace, sid) + + aces_size < CIFS_SID_BASE_SIZE) break; ace_size = le16_to_cpu(ace->size); - if (ace_size > aces_size) + if (ace_size > aces_size || + ace_size < offsetof(struct smb_ace, sid) + + CIFS_SID_BASE_SIZE) break; aces_size -= ace_size; granted |= le32_to_cpu(ace->access_req); @@ -1286,13 +1289,19 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path, ace = (struct smb_ace *)((char *)pdacl + sizeof(struct smb_acl)); aces_size = acl_size - sizeof(struct smb_acl); for (i = 0; i < le32_to_cpu(pdacl->num_aces); i++) { - if (offsetof(struct smb_ace, access_req) > aces_size) + if (offsetof(struct smb_ace, sid) + + aces_size < CIFS_SID_BASE_SIZE) break; ace_size = le16_to_cpu(ace->size); - if (ace_size > aces_size) + if (ace_size > aces_size || + ace_size < offsetof(struct smb_ace, sid) + + CIFS_SID_BASE_SIZE) break; aces_size -= ace_size; + if (ace->sid.num_subauth > SID_MAX_SUB_AUTHORITIES) + break; + if (!compare_sids(&sid, &ace->sid) || !compare_sids(&sid_unix_NFS_mode, &ace->sid)) { found = 1; -- 2.53.0