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=1792758652; b=xQivIiWU4TjKHwMkOFUJ51WSQOsWkXtJTAwlQkplnkV1j4OPFaqRlu600COW0ZE/Nh2R igX/svGw17CgQyv2mTxvSwzcxA5le4SGyaohQQN2aBwBiI1AIhfDA37pXR1zz23ihcurB AEzEbQiTlkzjjn0mACSpZVD1gYmRHRkkvjenXTQwkO3A0tDNYpP+6LGsYxgZuuGeeHGnA 866dqI4x84B9bffHDZjxNzO7eV/tCNWv8BmjBmFMQcao9KM0j2DbmpiF9+TCAVUpLvNYo lN3enrPpnWLLIFstJxtw17jlXepDlHCtGzrWn8QqA1OIEIiwH6HsD+M/7yRx525VqVg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792758652; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: Reply-To:MIME-Version:Lines:X-Developer-Signature:X-Developer-Key: Content-Transfer-Encoding; bh=/Fbgk5yCtOzXBShBKBsh1ekXKdyPhPpHnV9H1nGPb4E=; b=O8bxWFPnKBu1EDZpG4IiU+aevuHMCOx5l3F85Y/yg/P6JK8cTrVMsPiZOyKlGPf4roQy 7ODxnC5DY8D9WhEkauEsUz9sgUKVjVd1LTXa+SK67BRIyO+CAPSDC1GEfQv8eYpQuXcaH HrSZTo2V5hf9r1fe4B6ncEIXOD5+os04gbU3dB38Llf7dUGbqPOgUGKe6aZSvDvkuMT1d 7lUuIRlw7YznkN3wRMvZ7oArqqRKJq0eiJhx8QHBNn1IUTSikIWllr7QwyjkZWMfghoEc nMXAyGQ/78Mg6DeV8f97SYlrblcTfM+h1wTC83NkGqAZESIpRFjufg74R1uXt6K12ZA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=iKIt6sj0; 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 BFB5760A2619 for ; Fri, 23 Oct 2026 12:30:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=iKIt6sj0 Received: by smtp.kernel.org (Postfix) with ESMTPSA id B60601F031E1; Fri, 23 Oct 2026 12:30:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1792758651; bh=/Fbgk5yCtOzXBShBKBsh1ekXKdyPhPpHnV9H1nGPb4E=; h=From:To:Cc:Subject:Date:Reply-To; b=iKIt6sj0xFxiSCIiogvaIPCFvSm2ZB4edRefchDAhZ8zQgE4mqOTMfY+Weq2/aWXh zdUkR2hbhKtRKgjzL6R/JEw6Dy8G0z97J7XRi5SJgPbI3g1HLGlZS7Sm4Il+GrRydg syifnPUTSBuylZ/29Yu4O0xgGENDQczfvv1XUpwk= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-98990: namespace: check a submount for references right before unmounting it Date: Fri, 23 Oct 2026 14:19:52 +0200 Message-ID: <2026102315-CVE-2026-98990-e0d1@gregkh> X-Mailer: git-send-email 2.56.0 Reply-To: , X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4005; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=h+8MTULwhvMiaOMKcn34V5bjxTUeJoAzAB3gPb8xve4=; b=owGbwMvMwCRo6H6F97bub03G02pJDFm3Aw6vv2/y5SpPol6q4HVhz5T39/645EntfSSh2MG0l T8ovpOlI5aFQZCJQVZMkeXLNp6j+ysOKXoZ2p6GmcPKBDKEgYtTACZyXI5hwY71e51YPi3P+lh/ iau1cuaaxVL+qgzzjN1iJNrsk74fd5r4fs/Ua6/XHnU4BgA= 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: namespace: check a submount for references right before unmounting it shrink_submounts() and mark_mounts_for_expiry() first collect all the mounts they are allowed to unmount and then unmount them. Whether a mount is busy is decided by propagate_mount_busy() on the tree. But unmounting the first mount changes the tree that the second one propagates into. propagate_umount() moves a surviving overmount off a copy it unmounts and mounts it where the copy was mounted. If that's where the propagated copy of the second victim is looked up the overmount becomes a candidate of the second umount_tree(). It's childless and so trim_one() commits it without looking at its reference count. So a synchronous umount pulls out a busy mount that is in use somewhere else and marks it MNT_SYNC_UMOUNT while it has users: umount2(/tmp/plshrink/p1, 0) = 0 errno 0 cwd is (unreachable) The same two umounts requested one after the other fail with EBUSY. This needs a mount with MNT_SHRINKABLE, i.e., automounted submounts of NFS, AFS and CIFS or the tracefs mount below debugfs. Bind mounts inherit the flag. Check each mount right before it is unmounted under the same hold of namespace_sem and mount_lock as the umount itself. Make sure that the algorithm stays linear. The Linux kernel CVE team has assigned CVE-2026-98990 to this issue. Affected and fixed versions =========================== Issue introduced in 4.11 with commit 1064f874abc0d05eeed8993815f584d847b72486 and fixed in 6.6.160 with commit f6394281834492c6516a405a348b545ae698a331 Issue introduced in 4.11 with commit 1064f874abc0d05eeed8993815f584d847b72486 and fixed in 6.12.113 with commit 6e4012e571867868b545c91ca9d6095fdb709907 Issue introduced in 4.11 with commit 1064f874abc0d05eeed8993815f584d847b72486 and fixed in 6.18.57 with commit d73f04e92c1aab78d96ac6cadb234c8a3a373d22 Issue introduced in 4.11 with commit 1064f874abc0d05eeed8993815f584d847b72486 and fixed in 7.2.11 with commit 18902a23ef36f83d32bafc58ae2484e6bb4bb8ef Issue introduced in 4.11 with commit 1064f874abc0d05eeed8993815f584d847b72486 and fixed in 7.3 with commit 32bf92416614a1e3ff3524fc6b780259c7aad3ef Issue introduced in 4.1.40 with commit 5e6ef5ef6eaf690faad3a7c6c665ebf45d7b6ccf Issue introduced in 4.4.54 with commit 839d42687dfce0ed0ea2c6bd8d707cc0e276fbe7 Issue introduced in 4.9.15 with commit 808e83e5add13152bd4a88346487de68395c136b Issue introduced in 4.10.3 with commit 6de9d08a9718ee9c12ba6343c50141c2d633e3dc 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-2026-98990 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/namespace.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/f6394281834492c6516a405a348b545ae698a331 https://git.kernel.org/stable/c/6e4012e571867868b545c91ca9d6095fdb709907 https://git.kernel.org/stable/c/d73f04e92c1aab78d96ac6cadb234c8a3a373d22 https://git.kernel.org/stable/c/18902a23ef36f83d32bafc58ae2484e6bb4bb8ef https://git.kernel.org/stable/c/32bf92416614a1e3ff3524fc6b780259c7aad3ef