From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f49.google.com (mail-pj1-f49.google.com [209.85.216.49]) (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 D83333AA9EF for ; Mon, 6 Jul 2026 03:00:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.49 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783306817; cv=none; b=u30FgsMuErzFUfQw8TxzBrzlYFt72/0K8JJmJFXa7OcV7/bd5ru9tVbp7d29yPCRO36bswxrLOkADYJa1Orqo0q6T1ASDraK32wDyr+XNB08oYcg1WNFhz4cwYIUbUA9gj1QQ1XMPDUs1n+sUxmV2+lgZ+CNqRtJUs0Empudj6c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783306817; c=relaxed/simple; bh=1MChcVXg7jFJ+AFFxjeCXw4drRFFtdPukl/0eMPnQt0=; h=From:Date:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=sM3wr7X/61jFuklKpkvdxlG1hCxHhQ+Tztuq65GJqePnbweDnBuRtqFsQrVM8I+7PIEHy0APn+NTX8++hNrpJkukSrzXRW+qpEfNn51xgJDV7fpVmCWDXQIgpRHrve/C7o1c2Xz7emd/Lz/vzrlaUt+IYTSblAikrTFf+eXZO9E= 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=EvZ8KNW9; arc=none smtp.client-ip=209.85.216.49 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="EvZ8KNW9" Received: by mail-pj1-f49.google.com with SMTP id 98e67ed59e1d1-37cab825ec9so2372471a91.1 for ; Sun, 05 Jul 2026 20:00:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1783306810; x=1783911610; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:date:from:from:to:cc:subject :date:message-id:reply-to:content-type; bh=/Og2FoiMIHkhzxa96aH1wPvklWvZPI3x9dY/s87h4T8=; b=EvZ8KNW99ire9A9GpSKVGHDoUiOfPNvMYIm9A2H5C973Yuntyuhfut5MLjJoTH4wTL ZajXqxXpv66DtPA0E4ofpydf7J30K96YWBn8PdWRiEKRVpHp8nyALjCVWku5QbV2PLtz H1f7x9NCfWHtjYa61jswYETtm0zhePqyPAclc1NYScI9tC51QuITXvM4Nzx+QjHbMyvJ Ej1+H7Uv/mEHrBDi2npxHGiv9NybKRey8okZMcFkmcK6Fct+YP2SnVFx0Q4ZL2Q8+kAC 4oy7NKXV7Hwy4wR+WoEeQp7Vsn8OJFB+52LYV4/1BwAda0E5rTLBDlQim6sSM9daVLO7 BX0Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1783306810; x=1783911610; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:date:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=/Og2FoiMIHkhzxa96aH1wPvklWvZPI3x9dY/s87h4T8=; b=c9YSETw7IRq+sXN/WAuxBcg4kAs/bbU+yjgx9s+HiMRpPQa3DL4WzQQJNS2cUzjj5V uGOt7k0o1lnHfIrN9zt92bz/W4GSIhIa7kg+kHnpC162tElbCJErIP5erotAnelj9xZE EmXCErSve1/BBftFTqNAUWG79H9ZOaYL+P6LHRqh4D3kaBM8ss28HZv86N+F/JK0pdHR GLFy4Tc4KaVzAVD6VF9HKw6pLj2GZOcE2rQS2512pKbDGXE/QCUOrm1dEmmlgW0Dt5C8 5zwjnQVDp/O7m4xABue6Gg+mvMezWiExvZnsytB0XdRGxms83DXD1U8DQNq29YZx9sBn bHNw== X-Forwarded-Encrypted: i=1; AHgh+Rrm9+QvqrK3R0L4GpaMQlVtW6HILWHM4e07iUD8vdlBBqhgCTLgymfItZy1e2iuPr7QVL9dpyjjAgHc7FU=@vger.kernel.org X-Gm-Message-State: AOJu0YxloqG4O4GOGvC+gEQzwGFezYRbQjvqVymWF3bB5kjOXRGkm532 2XOj3qx/TKhhYUmEpvQAkvRMM/YMVAVLV/CYgAjed8fobv2502flvLs7 X-Gm-Gg: AfdE7cn+F2j5nqeOrSEK7TJQVd15RcAMqUNxFtirvViEbsLNS6+0eXx2MH91B6Jo8yi 2jsEAwnzkIGIdAgFqriIoBgzDx2HPWwwP66oWZMGgiywwcXTARtamTEtTTdr5K8zgXXhcJnHNTz gZWz1gdZeAL7gL/2btOLh41sUBq32xoEWtCm/8xzYAHxCgdDHX+kH+1lQ0ihA8bE2/v4AMzp7Wr uarVh/ByB9Sl6zIbLvcxe94yylv31l3DfuBjY2FyLhgUbw57Sv1lMYvJ3D10XbJYtrV+9JHeC2d 6xu+mumR9P3MywG+TeN6H/Nh6Y3zCvkXw3Q9i/5goU+J1Da/VKWS4jg5/mgfT10BfBFz6R4yxbw cDjOi+dAq0OsCG/AyGqICFR/KA++LLc1wXq6n76qn7aKd1LoeX32rL7vP1TF8sAcO66KXekPhOg emDjCbPg== X-Received: by 2002:a17:90b:2682:b0:381:21ea:9147 with SMTP id 98e67ed59e1d1-38281184e03mr9983981a91.13.1783306810305; Sun, 05 Jul 2026 20:00:10 -0700 (PDT) Received: from localhost ([2a09:bac5:55f0:18c8::278:41]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-31151fff32fsm12857601eec.21.2026.07.05.20.00.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 05 Jul 2026 20:00:09 -0700 (PDT) From: Coiby Xu X-Google-Original-From: Coiby Xu Date: Mon, 6 Jul 2026 10:59:40 +0800 To: Guangshuo Li Cc: Andrew Morton , Baoquan He , Mike Rapoport , Pasha Tatashin , Pratyush Yadav , Dave Young , Coiby Xu , kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] crash_dump: release keyring reference at the correct time Message-ID: References: <20260704112509.3717884-1-lgs201920130244@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260704112509.3717884-1-lgs201920130244@gmail.com> On Sat, Jul 04, 2026 at 07:25:09PM +0800, Guangshuo Li wrote: >restore_dm_crypt_keys_to_thread_keyring() gets a reference to the user >keyring before restoring the saved dm-crypt keys. > >The same keyring reference is then passed to add_key_to_keyring() for each >saved key, but add_key_to_keyring() drops that reference on every call. >This is only balanced when exactly one key is restored. With multiple >keys, the keyring reference is dropped too many times and may trigger a >refcount underflow or use-after-free. > >When more than five keys are restored, a refcount underflow/use-after-free >warning can be triggered. > >The early error paths after lookup_user_key() also return without dropping >the keyring reference. > >Keep ownership of the keyring reference in >restore_dm_crypt_keys_to_thread_keyring(), drop it once on all exit paths, >and make add_key_to_keyring() only use the reference without consuming it. > >Fixes: 62f17d9df692 ("crash_dump: retrieve dm crypt keys in kdump kernel") >Signed-off-by: Guangshuo Li >--- >v2: > - Mention the refcount underflow/use-after warning seen when restoring > more than five keys, as suggested by Coiby Xu. > - Order local variables in reverse Christmas tree style. > > kernel/crash_dump_dm_crypt.c | 15 ++++++++++----- > 1 file changed, 10 insertions(+), 5 deletions(-) > >diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c >index cb875ddb6ba6..c685497cd470 100644 >--- a/kernel/crash_dump_dm_crypt.c >+++ b/kernel/crash_dump_dm_crypt.c >@@ -81,7 +81,6 @@ static int add_key_to_keyring(struct dm_crypt_key *dm_key, > kexec_dprintk("Error when adding key"); > } > >- key_ref_put(keyring_ref); > return r; > } > >@@ -104,6 +103,7 @@ static int restore_dm_crypt_keys_to_thread_keyring(void) > struct dm_crypt_key *key; > size_t keys_header_size; > key_ref_t keyring_ref; >+ int ret = 0; > u64 addr; > > /* find the target keyring (which must be writable) */ >@@ -118,7 +118,8 @@ static int restore_dm_crypt_keys_to_thread_keyring(void) > dm_crypt_keys_read((char *)&key_count, sizeof(key_count), &addr); > if (key_count > KEY_NUM_MAX) { > kexec_dprintk("Failed to read the number of dm-crypt keys\n"); >- return -1; >+ ret = -1; >+ goto out; > } > > kexec_dprintk("There are %u keys\n", key_count); >@@ -126,8 +127,10 @@ static int restore_dm_crypt_keys_to_thread_keyring(void) > > keys_header_size = get_keys_header_size(key_count); > keys_header = kzalloc(keys_header_size, GFP_KERNEL); >- if (!keys_header) >- return -ENOMEM; >+ if (!keys_header) { >+ ret = -ENOMEM; >+ goto out; >+ } > > dm_crypt_keys_read((char *)keys_header, keys_header_size, &addr); > >@@ -137,7 +140,9 @@ static int restore_dm_crypt_keys_to_thread_keyring(void) > add_key_to_keyring(key, keyring_ref); > } > >- return 0; >+out: >+ key_ref_put(keyring_ref); >+ return ret; > } > > static int read_key_from_user_keyring(struct dm_crypt_key *dm_key) >-- >2.43.0 > > Hi Guangshuo, Thanks for addressing my feedback! Reviewed-and-tested-by: Coiby Xu -- Best regards, Coiby