From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm2-f13.google.com (mail-wm2-f13.google.com [74.125.225.141]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9E55019D8BC for ; Sat, 12 Sep 2026 09:54:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.225.141 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789206892; cv=none; b=B6jcTZdRuYCA0tHBZpwtv8aE6QmWV/FpM70hFgV1BvcccQCdSZ1DhDWvjnKPt3Yyg1Pjq3lcRktM6bHx46wf+PiGN8OukBi/1ZwtffFoT6h0Htzn2VyZPuaQchkUVDrA/oC65xL1odZJIjWBZaZDE3cFPAlMudmSrrFfH9eqlmQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789206892; c=relaxed/simple; bh=xLGZ6pfrGi7Y0P4Mp+UYTrV0Mv1NTPoX6SsMuAFVEFY=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=hZ4J4N5xzFnu72yzRNfl+afndSdidMGnILINGfaULQX546LlYVndxrhG6orreVShOZURy4da5KjvlrWQ4UKpr5UI1k8Z2u1WGCRjaBykZT5EXVz/ouBZMu/zt82JPIf6QRERLELrtKYigejR+8n7zUlxKUYFyBTD9RJ1xeMjiqU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=YQRcTUGR; arc=none smtp.client-ip=74.125.225.141 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="YQRcTUGR" Received: by mail-wm2-f13.google.com with SMTP id 5b1f17b1804b1-49e6b885ef8so2006215e9.1 for ; Sat, 12 Sep 2026 02:54:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1789206889; x=1789811689; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to:content-type; bh=KnNpw1WOa9p3MlCBG6ZZCFsfq25XNP5JJbLzPV5Kleo=; b=YQRcTUGRgJG63ylGSvwLq9lvUJSzb6MmR8xxznYtZHOZx2ydHGJlkrbEUtO/TEeM5X Y6P0hxK3/5Wj0k3xMfnZUdJdw9+Nk7FyuFy7PlWodrfGvX1zVBSwIBqA8gq/tD/viXI1 Icy9Z19vkv/lB6FxfydG5l5A/HCS1gCGLT1bob3jaqpGAVonEIt6AHJ67mS/95VE+YZ0 g3vNezzDlTcnJ4YydGXiWGxZRH3IzB4udOKuhce+jkSdveykWBS+FmBoK4f7wvrpLhVT QKWODaPEogClLGgHP3LCcNnr/LDsGraYo1ZX1rcCGAVKd8q6/BRxLmU8byMDt0uJZ25f dBMg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1789206889; x=1789811689; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=KnNpw1WOa9p3MlCBG6ZZCFsfq25XNP5JJbLzPV5Kleo=; b=XB32GGYNCEym5tziUtzMLjhuOMwAlFj4+kHLjC2B2fzMno82bRXXws4vEtNGpbzVIX bmd+3gI0KyMby9Guty2VuEElDjhJ4hzWSfbRGOmaNElpHerZiHtz1/ENliDGR/HUQIfS S1G20zzXcKztUz82OvyaSROBKCXda08jIc69WwApzw9ZkGzacgO9KK2BzpMZJWNASGlK HEFUibwmkjwA3gpiPP2kRQm/9ONXrayo8WZCNsNg8nAAkMfT0RurxETfCDP32rEgC6mk m9oCc9GZKEq1n8CyHe2lbELCRsPUZ9v9Mv0OXPYBtTXZ9U3Bhk6UHjSiuXFF/f2yQ+Cn DSxQ== X-Forwarded-Encrypted: i=1; AKwUvBybRVLgmWFBhDRgd7eOZxm4CnXcuxxt45ztPSfyOKoVJzY/9Dqok4RloH5MgFNk6XUoHwjW3qHV9XbHbQbJsMXxDZERVMI=@vger.kernel.org X-Gm-Message-State: AFuF++nT9F7ISign1kAn5teVtg9Eg3SndYHPBtyv9fTblBVUXc1Hks39 oPrpTKsP/hVMudi7uIKPxSwTe40EuJpOTO/QydJa7g4Y17f3c0/Sw/0r X-Gm-Gg: AYBFou3IXDRcG5frL/uX+qwBzaneACJ3jjg30uJkEcHREty/B6z9jcrcDcru1vqA5WJ efp/YR41Iwg0p2eItBeqsxrzUe7aCkXzW6Iu133wZo8hTHa4A58OTWxdVewWce17wMwyBIyj7D+ zkXmJhvCEqhAqmva7x219CCKMgxmNA8aNQ9Tw6jWuhUhCvmBdLTnYZoRAxYDXxyqxY8j4EBjpTh N8ryIxUQgPutTs15rtaEg9+RuN5fsDO9ipRu49Q9wnF/iVu0Rbb/o3nX4z5KBNsN+8rzZa4wTUp 0YTSIoNX0jW2BNMwcFvf4enHe+ckeLZbfGK4g2SZRfdtyxbw7cADbDeRkdbsHxZ4OUVim/2wxj8 SK47dfIsw9J5NU7QHcuiHmsuu5nSjb/iY+odrr03PRxgJTuDdSOQM3R4AWXf8rluVidjBPM+CTb 3K6glKh1dyqj0fznQlicg06dGgnLKKd8v04YNOFsTjpZ3Cb1mU9Q6KE0TyJoh9rFaOozpmNyFhF Lu7cvYSJ9iPmzjPQ//QjM1XJ0ntcNnw7UnXhGDUcpL7o00GXP1b2d/frs8heDJUqz6QjQ8Mb0eu 1hPURzqg+mkGVZRB8wb8GSWZ5MY1khb/u7Ya603sDAdX/XUxBWSBZ9+9KihDiUTCd62FbYGrvkn J8A== X-Received: by 2002:a05:600d:4452:20b0:499:b65d:124f with SMTP id 5b1f17b1804b1-49e6198c2aemr67076425e9.11.1789206888615; Sat, 12 Sep 2026 02:54:48 -0700 (PDT) Received: from localhost.localdomain (dynamic-2a02-3100-b260-f201-9983-e8c4-aff5-7a36.310.pool.telefonica.de. [2a02:3100:b260:f201:9983:e8c4:aff5:7a36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49e71adc2ecsm15179175e9.4.2026.09.12.02.54.47 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sat, 12 Sep 2026 02:54:48 -0700 (PDT) From: Karl Mehltretter To: David Howells , Jarkko Sakkinen Cc: Karl Mehltretter , Paul Moore , James Morris , "Serge E. Hallyn" , keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v4] keys: finalize persistent keyring timeout after link attempt Date: Sat, 12 Sep 2026 11:54:40 +0200 Message-Id: <20260912095440.79864-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When no keyring exists for the requested UID, KEYCTL_GET_PERSISTENT creates and registers one before linking it to the requested destination. The configured timeout is set only after the destination link succeeds. A destination restricted with KEYCTL_RESTRICT_KEYRING makes that link fail with -EPERM. With persistent_keyring_expiry set to 60 seconds, /proc/keys still reports the registered keyring's expiry as "perm". The failed call therefore leaves a quota-exempt keyring in the namespace's hidden register, where it may remain until namespace teardown. Rename the write-locked helper to key_get_or_create_persistent() and return the key reference through a result parameter. Return 0 when it creates a keyring and 1 when the retry finds an existing one. Return a negative error on failure. Another caller may create the keyring between the initial read-locked lookup and the retry under the write lock. Set the timeout after permission checking and linking. Do this on success, or on failure if the call allocated the keyring. This leaves a new keyring collectible after failure without starting its timeout while linking is still in progress. Fixes: f36f8c75ae2e ("KEYS: Add per-user_namespace registers for persistent per-UID kerberos caches") Assisted-by: LLM Signed-off-by: Karl Mehltretter --- Changes in v4: - tweak comment (Jarkko) v3: https://lore.kernel.org/r/20260901191743.39210-1-kmehltretter@gmail.com/ Changes in v3: - Return the persistent key reference through a result parameter (Jarkko). - Keep lookup-or-create atomic inside the helper and use 0 for creation, 1 for an existing keyring, and negative values only for errors. v2: https://lore.kernel.org/r/20260901164323.35785-1-kmehltretter@gmail.com/ Changes in v2: - Rewrite the commit message around the restricted-destination reproducer and trim the explanation (Jarkko). - Track whether the persistent keyring was newly allocated and finalize its timeout after the permission and link checks. This preserves an existing keyring's timeout on failure and avoids expiry during linking. Testing below was performed for v3; v4 changes only the comment. Tested with QEMU 10.2.1 TCG on i386 and x86_64. With persistent_keyring_expiry set to 60 seconds, KEYCTL_GET_PERSISTENT returned -EPERM and /proc/keys reported "perm" before the fix and "1m" after it on both architectures. Also tested on x86_64 with persistent_keyring_expiry set to 1 second and gc_delay set to 0. Successful calls reused the same serial, a newly created keyring from a failed call expired, and a failed call using an existing keyring left its timeout unchanged. A test-only two-second delay before timeout finalization did not allow the keyring to be collected before link. Two concurrent callers returned the same serial. A test-only 100 ms delay after the read-locked miss forced both callers into the write-locked retry and confirmed that the second caller took the 1 (existing) return path. security/keys/persistent.c | 55 ++++++++++++++++++++++---------------- 1 file changed, 32 insertions(+), 23 deletions(-) diff --git a/security/keys/persistent.c b/security/keys/persistent.c index 97af230aa4b22..bdab995393261 100644 --- a/security/keys/persistent.c +++ b/security/keys/persistent.c @@ -33,25 +33,31 @@ static int key_create_persistent_register(struct user_namespace *ns) } /* - * Create the persistent keyring for the specified user. + * Get or create the persistent keyring for the specified user. * * Called with the namespace's sem locked for writing. + * + * Returns a boolean indicating whether the keyring already existed, + * or a negative error. On success, *persistent_ref holds a reference + * to the keyring. */ -static key_ref_t key_create_persistent(struct user_namespace *ns, kuid_t uid, - struct keyring_index_key *index_key) +static int key_get_or_create_persistent(struct user_namespace *ns, kuid_t uid, + struct keyring_index_key *index_key, + key_ref_t *persistent_ref) { struct key *persistent; - key_ref_t reg_ref, persistent_ref; + key_ref_t reg_ref; if (!ns->persistent_keyring_register) { - long err = key_create_persistent_register(ns); + int err = key_create_persistent_register(ns); + if (err < 0) - return ERR_PTR(err); + return err; } else { reg_ref = make_key_ref(ns->persistent_keyring_register, true); - persistent_ref = find_key_to_update(reg_ref, index_key); - if (persistent_ref) - return persistent_ref; + *persistent_ref = find_key_to_update(reg_ref, index_key); + if (*persistent_ref) + return 1; } persistent = keyring_alloc(index_key->description, @@ -61,9 +67,10 @@ static key_ref_t key_create_persistent(struct user_namespace *ns, kuid_t uid, KEY_ALLOC_NOT_IN_QUOTA, NULL, ns->persistent_keyring_register); if (IS_ERR(persistent)) - return ERR_CAST(persistent); + return PTR_ERR(persistent); - return make_key_ref(persistent, true); + *persistent_ref = make_key_ref(persistent, true); + return 0; } /* @@ -78,6 +85,7 @@ static long key_get_persistent(struct user_namespace *ns, kuid_t uid, key_ref_t reg_ref, persistent_ref; char buf[32]; long ret; + bool created = false; /* Look in the register if it exists */ memset(&index_key, 0, sizeof(index_key)); @@ -100,23 +108,24 @@ static long key_get_persistent(struct user_namespace *ns, kuid_t uid, * also need to create the register. */ down_write(&ns->keyring_sem); - persistent_ref = key_create_persistent(ns, uid, &index_key); + ret = key_get_or_create_persistent(ns, uid, &index_key, + &persistent_ref); up_write(&ns->keyring_sem); - if (!IS_ERR(persistent_ref)) - goto found; - - return PTR_ERR(persistent_ref); + if (ret < 0) + return ret; + created = ret == 0; found: + persistent = key_ref_to_ptr(persistent_ref); ret = key_task_permission(persistent_ref, current_cred(), KEY_NEED_LINK); - if (ret == 0) { - persistent = key_ref_to_ptr(persistent_ref); + if (ret == 0) ret = key_link(key_ref_to_ptr(dest_ref), persistent); - if (ret == 0) { - key_set_timeout(persistent, persistent_keyring_expiry); - ret = persistent->serial; - } - } + + if (ret == 0 || created) + key_set_timeout(persistent, persistent_keyring_expiry); + + if (ret == 0) + ret = persistent->serial; key_ref_put(persistent_ref); return ret; base-commit: 08dbfad3f5040f5bdb6c529da20d6d4e81fefd72 -- 2.53.0