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 8BB63221FB6 for ; Sat, 23 May 2026 16:52:40 +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=1779555161; cv=none; b=mX+xxoA2jzb9s0Hqa6owMYPRjYZYy/80opUvYp6kfi6IYlKbWRssQ6g4B9en+vJ/OsZ662fIl8Bb8f/4QJPCdo1K6nthGNcjJNHyb/wd8iPNdS5fBX1GaO3OXqNyy5gKiIM6ajNkEj18gfD+G6k26Zf5ifo3xExEHV7frP5I3U8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779555161; c=relaxed/simple; bh=tNixGLk/kHI+rRk29OiHg7VCLfhrEZEjsKn/9rXhn9s=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=uexZSceYQKP8PIH+EHRmtNRfBknBEMNRPgGnInsAYWRb+Y9g5LacRYicW5Ueyj86jTj2Gg2X1rDabfGrxfkEknu4EqnzvrFtcnaaZrhPu4yv5qWu+7s0f7G7ofkvKMfCRD448elT0Z/89YCEsWb1rpPs+BMzWbIH4pOOM2f6cZI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NuhqxF+c; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NuhqxF+c" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8312B1F000E9; Sat, 23 May 2026 16:52:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779555160; bh=0jP8nTyRtg0rkBk4SpSIH5+VkUx1g4zqZ9hM0xx+gw8=; h=From:To:Cc:Subject:Date; b=NuhqxF+cRNpIsqZg7ahb+osq/uCyEekk1HytHLBLt0yJ9nb6xhua5W/3g7VcUNE1K bInZEH9XrkNkJx/z/bmxewCRM3hRIIZYH/hXG5XWGPoLrv74U18BzReZ/fb/BR34Px zu0CmYHHbyaOVPLxDBSxnTmoxRnuFD7dqWXPtwBchzIkXvwVozdr+E4npnB9qEF6pO 75u0fSqP2FsQxtmgGJxI2zdW9rxuxiIurhNmwiECK/BWaxfJD9QlimMSotxHk0h1hy D+fAaDAvmdWkO75OxechN3ZsAZ7Yssar0i6eGF7eIWfV4twEzY1fBayu4DsUfE7bmw yvVSDPYJKe+YQ== From: Chuck Lever To: NeilBrown , Jeff Layton , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: , Chuck Lever , Chris Mason Subject: [PATCH] SUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2 Date: Sat, 23 May 2026 12:52:37 -0400 Message-ID: <20260523165237.510204-1-cel@kernel.org> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Chuck Lever 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") Signed-off-by: Chuck Lever --- 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 b5fb70419faa..4d12d49434c2 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; -- 2.54.0