From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from frasgout11.his.huawei.com (frasgout11.his.huawei.com [14.137.139.23]) (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 46E783264CD; Fri, 24 Apr 2026 08:30:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=14.137.139.23 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777019413; cv=none; b=F4ONHXypbquPJ9ME+cVe4qnHlZTulxQApqSZOyHrl4KxALGZxzHB2/OEWYnx/Yitwcsb1SVj9EBvVwLHV8ZcNZvsNEMm8RzOu5qa3SrHvn3DCTo0CSWOAI5TmY334vwa6PM8dCi2WMpp9e+BQnltCqY6I0PjKCbRl4djw0oSNpE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777019413; c=relaxed/simple; bh=mN9hKJgOIbUIgtW7CMIeUWc8FjfE9DZDmZHij53WAW8=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Owt5KLQ0fyFuxJA5B2i4mBcyoNoKz553utMrCwRcpu5F9J7ErojhBomPxOlSc+hGXaYuGRFqrhLj2VE4K5k+wukEirGBrudeqQ9SCXc+XKFGOROZwXOPHjDANGjDIHXoc0QWkz1dF9ueWUmLRFtswQhafGIzne1FpZI2o9498FQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=14.137.139.23 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.18.224.235]) by frasgout11.his.huawei.com (SkyGuard) with ESMTPS id 4g25GT0PPcz1HCH8; Fri, 24 Apr 2026 16:09:37 +0800 (CST) Received: from mail02.huawei.com (unknown [7.182.16.27]) by mail.maildlp.com (Postfix) with ESMTP id 10F3E40571; Fri, 24 Apr 2026 16:14:01 +0800 (CST) Received: from [10.204.63.22] (unknown [10.204.63.22]) by APP2 (Coremail) with SMTP id GxC2BwAXwe08JutpXnDKAA--.10970S2; Fri, 24 Apr 2026 09:14:00 +0100 (CET) Message-ID: <1cbfa3d83a3ae9db393fe23d677c282090c59146.camel@huaweicloud.com> Subject: Re: [PATCH v3] evm: terminate and bound the evm_xattrs read buffer From: Roberto Sassu To: Pengpeng Hou , Mimi Zohar Cc: Roberto Sassu , Dmitry Kasatkin , Eric Snowberg , Paul Moore , James Morris , Serge Hallyn , linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 24 Apr 2026 10:13:46 +0200 In-Reply-To: <20260424070101.1-evm-v3-pengpeng@iscas.ac.cn> References: <20260417223004.1-evm-xattrs-v2-pengpeng@iscas.ac.cn> <20260424070101.1-evm-v3-pengpeng@iscas.ac.cn> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CM-TRANSID:GxC2BwAXwe08JutpXnDKAA--.10970S2 X-Coremail-Antispam: 1UD129KBjvJXoW7ZFy3Cr4fWw43uF18ur4rKrg_yoW8Kr13pF Z8t3WDJFn5XryDGFW5JF17u393G3y8GFWUGrn3Gw12vasxXr9agrykKa4ruFyrJr40yw45 t3s0kFnIyw1Yq3DanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvjb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Jr0_JF4l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr0_Cr1l84ACjcxK6I8E87Iv67AKxVWUJVW8JwA2z4x0Y4vEx4A2jsIEc7CjxV AFwI0_Gr0_Gr1UM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40E x7xfMcIj6xIIjxv20xvE14v26r1j6r18McIj6I8E87Iv67AKxVWUJVW8JwAm72CE4IkC6x 0Yz7v_Jr0_Gr1lF7xvr2IY64vIr41lFIxGxcIEc7CjxVA2Y2ka0xkIwI1lc7CjxVAaw2AF wI0_Jw0_GFyl42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4 xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43 MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I 0E14v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWU JVW8JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjxUF1 v3UUUUU X-CM-SenderInfo: purev21wro2thvvxqx5xdzvxpfor3voofrz/1tbiAgANBGnrE4cBqgAAs2 On Thu, 2026-04-23 at 23:30 +0800, Pengpeng Hou wrote: > evm_read_xattrs() allocates size + 1 bytes, fills them from the list of > enabled xattrs, and then passes strlen(temp) to > simple_read_from_buffer(). When no configured xattrs are enabled, the > fill loop stores nothing and temp[0] remains uninitialized, so strlen() > reads beyond initialized memory. >=20 > Explicitly terminate the buffer after allocation, use snprintf() for > each formatted line, and pass the accumulated length, without risk of > truncation, to simple_read_from_buffer(). >=20 > Fixes: fa516b66a1bf ("EVM: Allow runtime modification of the set of verif= ied xattrs") > Signed-off-by: Pengpeng Hou Reviewed-by: Roberto Sassu Thanks Roberto > --- > Changes since v2: > - adjust the changelog wording to mention why the accumulated length is > safe > - add the blank line after the allocation error path > - add a comment explaining why snprintf() cannot truncate in the fill loo= p >=20 > diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/= evm_secfs.c > index acd840461902..4baf5e23bc97 100644 > --- a/security/integrity/evm/evm_secfs.c > +++ b/security/integrity/evm/evm_secfs.c > @@ -127,8 +127,8 @@ static ssize_t evm_read_xattrs(struct file *filp, cha= r __user *buf, > size_t count, loff_t *ppos) > { > char *temp; > - int offset =3D 0; > - ssize_t rc, size =3D 0; > + size_t offset =3D 0, size =3D 0; > + ssize_t rc; > struct xattr_list *xattr; > =20 > if (*ppos !=3D 0) > @@ -151,16 +151,22 @@ static ssize_t evm_read_xattrs(struct file *filp, c= har __user *buf, > return -ENOMEM; > } > =20 > + temp[size] =3D '\0'; > + > + /* > + * No truncation possible: size is computed over the same enabled > + * xattrs under xattr_list_mutex, so offset never exceeds size. > + */ > list_for_each_entry(xattr, &evm_config_xattrnames, list) { > if (!xattr->enabled) > continue; > =20 > - sprintf(temp + offset, "%s\n", xattr->name); > - offset +=3D strlen(xattr->name) + 1; > + offset +=3D snprintf(temp + offset, size + 1 - offset, "%s\n", > + xattr->name); > } > =20 > mutex_unlock(&xattr_list_mutex); > - rc =3D simple_read_from_buffer(buf, count, ppos, temp, strlen(temp)); > + rc =3D simple_read_from_buffer(buf, count, ppos, temp, offset); > =20 > kfree(temp); > =20