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 BC99558F067 for ; Fri, 11 Sep 2026 20:03:07 +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=1789157006; cv=none; b=VPfyhuuYwY+tHlfAqy3Suw6/U/dPhXJbOHuZzSSMUDKuCjQlyXgt1qXWaFqdyPOzC9VTTe42j75YL5vKcL78XTEFw/iSJCcdYTaln8IrrkWffL1l1dkK0ktBy0zMRv+vAkmuNZWM2VZTyCho1oRgtj99BO44d2TsQlpN6z+FfdM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789157006; c=relaxed/simple; bh=TJQHYAjsnP1pDhvpK+lgfsF5b+blMbgWCbKx83n4S3k=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=KqwJyaPmyYQT5LZTdjwjN/TUQ4PkuGRstr8V0EovJKkXq8DftpI350QwZ1haJT21dj6nIHTlrUNTQ2DK+DttpFg3psej7oaGJVCiMqfdnLnaxbeWlzMA5f/zXqDqDzhcx/hx8tjGK+tSFLMgfJ8Uy7/c2jsY7xLoJMIuxrqoZ4c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=IVHyi6Xq; 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="IVHyi6Xq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 415BC1F0089B; Fri, 11 Sep 2026 20:03:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789156981; bh=SvpnUVQuX3zy5CgrP+ycjyadXz8Et1YVh2UgYaIaE+g=; h=From:To:Cc:Subject:Date:Reply-To; b=IVHyi6XqBJI4BTN0QDQPTu9DXECU6fsXV/S2JZx6QtmqOMB4sg3aBM731sDERxCBS l07KidZ5IjDDOFJp0Jg2LZ3eAjqSWOYOFbxSUSfLyL/UZAvlOavc46R/3AdtYuvuj1 H50FGxLRGkMvStpsw0v17k/YA6Mrv7gtioq9UBnk= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-89696: nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref Date: Fri, 11 Sep 2026 21:46:25 +0200 Message-ID: <2026091154-CVE-2026-89696-ecb8@gregkh> X-Mailer: git-send-email 2.55.0 Reply-To: , Precedence: bulk X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3464; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=0yrFieFwcvI0KVsF4gtORCszRSRzqcpT/4udwemWV58=; b=owGbwMvMwCRo6H6F97bub03G02pJDFlLIpuicvf8PPcpmG3+F8sFl63OHYt2u7pMmsd+0jvv8 z5OpQX2HbEsDIJMDLJiiixftvEc3V9xSNHL0PY0zBxWJpAhDFycAjARhwyGBYc7vmz7fUdPzKC7 9W2JrUP/imtHlzMsuGRw20BZrKi00NJm3sYp+/eyOp2VBAA= X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Transfer-Encoding: 8bit From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref When CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return success with fh_dentry and fh_export both NULL if fh_verify() returns nfserr_stale and putfh->no_verify is true. The NFSD4_FH_FOREIGN flag is set, but the compound dispatch loop only uses this flag to bypass the nfserr_nofilehandle check -- it does not prevent subsequent ops from running with a NULL fh_dentry. A remote client can exploit this by crafting a COMPOUND that includes an inter-SSC COPY (which causes check_if_stalefh_allowed() to set no_verify=true on the saved PUTFH) with an additional op inserted between the source PUTFH and SAVEFH. For example, SETATTR calls fh_want_write() which dereferences fh_export->ex_path.mnt without calling fh_verify() first, causing a NULL pointer dereference in the nfsd kthread. Fix this by gating the dispatch loop: when NFSD4_FH_FOREIGN is set and fh_dentry is NULL, only OP_SAVEFH (needed for the inter-SSC flow) and ops with ALLOWED_WITHOUT_FH (which don't need a resolved filehandle) may proceed. All other ops receive nfserr_stale, per RFC 7862 Section 15.2.3 which specifies that foreign filehandle validation is deferred to the consuming operation and NFS4ERR_STALE returned at that point. The Linux kernel CVE team has assigned CVE-2026-89696 to this issue. Affected and fixed versions =========================== Issue introduced in 5.6 with commit b9e8638e3d9ed8334f1f7071e081860aac37e83e and fixed in 6.12.109 with commit 35f248bd40b47b229d4999581df45b97daadd977 Issue introduced in 5.6 with commit b9e8638e3d9ed8334f1f7071e081860aac37e83e and fixed in 6.18.50 with commit 311f7d926630940650447cbd1c932b076b40a6c4 Issue introduced in 5.6 with commit b9e8638e3d9ed8334f1f7071e081860aac37e83e and fixed in 7.2.4 with commit bf4d338dc8625d70c7f2cb0657d66851a7ac9154 Issue introduced in 5.6 with commit b9e8638e3d9ed8334f1f7071e081860aac37e83e and fixed in 7.3-rc1 with commit c59738a00aa51b16adc1b5ceb7c80877168efb4d Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2026-89696 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: fs/nfsd/nfs4proc.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/35f248bd40b47b229d4999581df45b97daadd977 https://git.kernel.org/stable/c/311f7d926630940650447cbd1c932b076b40a6c4 https://git.kernel.org/stable/c/bf4d338dc8625d70c7f2cb0657d66851a7ac9154 https://git.kernel.org/stable/c/c59738a00aa51b16adc1b5ceb7c80877168efb4d