From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 253F54EE858; Tue, 13 Oct 2026 12:18:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791893907; cv=none; b=GtvtbnbyAAlLm0xoa+AEgVMhk5jv1MiHtqtIRTmpAqjHycBoSONM7NvlMe4DKPZFHGC8NoJVVV0NbnM6qVW14g8inErDKhLBrFZL07Uvcjp1nNF/ppJmJdw6p89pBuXahF4VnxLNxPbwQAFFJiKsfmdmlN9yivdNEvgLUReb+do= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791893907; c=relaxed/simple; bh=ptivWu3L1EetIwU4pTWnIc4CdZoACzDe5B8Q8O4l5/0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=sLxMiQHG3zeGgPnALX9i6ddL5A7PbbIprBhj6BuoShcXQ1Ldz3MseW661Vt4dpas+6GUEw9UrevAJfw2Q9tZOthY9InSN7te2DdU1GLJaS1qrz7EdMyd9lwchuXzJUVWnSbM171Qb1b151sWrQyliFlVlMnOt0a2VqhFF3mg1c4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=hFE5kZnm; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="hFE5kZnm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78F961F000FF; Tue, 13 Oct 2026 12:18:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791893906; bh=15C0YlzZbXg3+ii0OAf+NGg34r7LV9W2lrs7XO2rvCw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=hFE5kZnmHKKUNEGrjzODrUFk9I02ltxan2bPFq9SZCGhl6+jKajpfsnPVGjb3cRyg 9wycf0ujCL6n9naz7lnjRvhTH7xfXdy0EltiL3a7CtZwocQz5hlYgNsQQeg6nycc3W iuWTjAsYD9jTvI+2jv/O99E1KHk8FH5bLWpLh1Q4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chris Mason , Jeff Layton , Chuck Lever , Sasha Levin Subject: [PATCH 6.18 381/621] SUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2 Date: Tue, 13 Oct 2026 13:36:16 +0200 Message-ID: <20261013112929.886672318@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261013112920.855194808@linuxfoundation.org> References: <20261013112920.855194808@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Chuck Lever [ Upstream commit b94f6719dcd9f7a609bc5f459f85795900e77d25 ] gss_krb5_verify_mic_v2() reads the token ID at ptr[0..1], the flags byte at ptr[2], and padding at ptr[3..7], then passes ptr + GSS_KRB5_TOK_HDR_LEN and cksum_len to gss_krb5_mic_build_sg(). None of these accesses check read_token->len first. The minimum safe token size is GSS_KRB5_TOK_HDR_LEN (16) plus ctx->krb5e->cksum_len (12-24, depending on the enctype). All callers accept shorter tokens from the wire: - gss_unwrap_resp_integ() enforces only an upper bound (offset + len <= rcv_buf->len) before allocating mic.data = kmalloc(len) and passing it to gss_verify_mic(). A malicious NFS server can therefore supply a short checksum opaque, producing a small slab allocation that the Kerberos MIC verifier reads past. - gss_validate() enforces only len <= RPC_MAX_AUTH_SIZE (400) before passing the wire-supplied length to gss_validate_seqno_mic(), which constructs a mic xdr_netobj and calls gss_verify_mic(). - svcauth_gss_verify_header() enforces only checksum.len >= XDR_UNIT (4 bytes) before dispatching to gss_verify_mic(). - svcauth_gss_unwrap_integ() checks only that the checksum fits in gsd->gsd_scratch. Add a length guard at the top of gss_krb5_verify_mic_v2(), before any ptr[] access or scatterlist construction. Well-formed MIC tokens from gss_krb5_get_mic_v2() already have exactly GSS_KRB5_TOK_HDR_LEN + cksum_len bytes, so valid traffic is unaffected. Reported-by: Chris Mason Fixes: de9c17eb4a91 ("gss_krb5: add support for new token formats in rfc4121") Cc: stable@vger.kernel.org Reviewed-by: Jeff Layton Link: https://patch.msgid.link/20260523165237.510204-1-cel@kernel.org Signed-off-by: Chuck Lever Signed-off-by: Sasha Levin --- net/sunrpc/auth_gss/gss_krb5_unseal.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/sunrpc/auth_gss/gss_krb5_unseal.c b/net/sunrpc/auth_gss/gss_krb5_unseal.c index b5fb70419faaa..4d12d49434c28 100644 --- a/net/sunrpc/auth_gss/gss_krb5_unseal.c +++ b/net/sunrpc/auth_gss/gss_krb5_unseal.c @@ -89,6 +89,9 @@ gss_krb5_verify_mic_v2(struct krb5_ctx *ctx, struct xdr_buf *message_buffer, dprintk("RPC: %s\n", __func__); + if (read_token->len < GSS_KRB5_TOK_HDR_LEN + cksum_len) + return GSS_S_DEFECTIVE_TOKEN; + memcpy(&be16_ptr, (char *) ptr, 2); if (be16_to_cpu(be16_ptr) != KG2_TOK_MIC) return GSS_S_DEFECTIVE_TOKEN; -- 2.53.0