From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7F078ECAAD8 for ; Fri, 16 Sep 2022 17:30:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229743AbiIPRab (ORCPT ); Fri, 16 Sep 2022 13:30:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60806 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229633AbiIPRaa (ORCPT ); Fri, 16 Sep 2022 13:30:30 -0400 Received: from smtp-8fa8.mail.infomaniak.ch (smtp-8fa8.mail.infomaniak.ch [IPv6:2001:1600:4:17::8fa8]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 89C029D667 for ; Fri, 16 Sep 2022 10:30:27 -0700 (PDT) Received: from smtp-3-0000.mail.infomaniak.ch (unknown [10.4.36.107]) by smtp-3-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4MTh0x4t6XzMpvb5; Fri, 16 Sep 2022 19:30:25 +0200 (CEST) Received: from ns3096276.ip-94-23-54.eu (unknown [23.97.221.149]) by smtp-3-0000.mail.infomaniak.ch (Postfix) with ESMTPA id 4MTh0w5gprz3j; Fri, 16 Sep 2022 19:30:24 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=digikod.net; s=20191114; t=1663349425; bh=c3cQ5OIpUdQA4LPM1JRC0JMRXf8FmbTv1tLsYfxYLC8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=bilt7jZgBPz8hIBzuvh776xOvi2/R06WBHtNwyFUSGxpMl3uGJDKUzOSzpbofIDU1 xWcqDJNYlysRopa5ZZzAVOf7L+axtZ+LsmqlWpa7ujih1Np6kQ/b8DCgQvYGdb0RBz 3sbrYgF5gN3gSq/ZHPAA0pNf+6OeqFaEot7qAKS8= Message-ID: <962b121b-b299-e024-bf3d-8cc6e12e01f7@digikod.net> Date: Fri, 16 Sep 2022 19:30:24 +0200 MIME-Version: 1.0 User-Agent: Subject: Re: [PATCH v6 1/5] security: create file_truncate hook from path_truncate hook Content-Language: en-US To: =?UTF-8?Q?G=c3=bcnther_Noack?= , Namjae Jeon , David Howells , Christian Brauner Cc: James Morris , Paul Moore , "Serge E . Hallyn" , linux-fsdevel@vger.kernel.org, Konstantin Meskhidze , linux-security-module@vger.kernel.org References: <20220908195805.128252-1-gnoack3000@gmail.com> <20220908195805.128252-2-gnoack3000@gmail.com> From: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: We may indeed need to change fs/open.c:vfs_truncate() because of these different call sites. I'm not sure how these subsystems work though. On 08/09/2022 22:28, Günther Noack wrote: > Adding Namjae Jeon and David Howells as authors of the respective > files in fs/ksmbd and fs/cachefiles -- do you happen to know whether > these vfs_truncate() calls are using 'struct file's that are opened by > normal userspace processes, where LSM policies may apply? > > P.S. In this patch I have looked for all places where the > security_path_truncate() hook was called, to see which of these should > rather use security_file_truncate() (and I made sure that it does the > same thing for all the LSMs that use it). > > I'm confident that this does the right thing when truncate() or > ftruncate() are called from userspace, but one of the places that > still calls the path-based hook is vfs_truncate(), and this is called > from more places in the kernel than just from userspace: > > init/initramfs.c > 387: vfs_truncate(&wfile->f_path, body_len); > > security/keys/big_key.c > 172: vfs_truncate(&payload->path, 0); > > fs/cachefiles/interface.c > 242: ret = vfs_truncate(&file->f_path, dio_size); > > fs/cachefiles/namei.c > 497: ret = vfs_truncate(&path, ni_size); > > fs/ksmbd/smb2pdu.c > 2350: int rc = vfs_truncate(path, 0); > > fs/ksmbd/vfs.c > 874: err = vfs_truncate(&filp->f_path, size); > > I suspect that these are benign but am not familiar with all of these > corners of the codebase. -- The question is: Some of these call > vfs_truncate() on the f_path of an existing struct file -- should > these rather be calling the security_file_truncate() than the > security_path_truncate() hook to authorize the truncation? > > Specifically, I think: > > * initramfs happens at system startup and LSMs should not interfere at > this point yet > * security/keys does not use an opened struct file, so calling the > path-based hook through vfs_truncate() is correct > * fs/cachefiles and fs/ksmbd use the file system from the kernel to > expose it as another file system (in a cached form for cachefiles, > and over the network for ksmbd). I suspect that these file systems > are not handling 'struct file's which are opened in contexts where a > LSM applies? It that a reasonable assumption? I think you're right but I have some doubts about the cachefiles subsystem. I don't know how ksmb deals with these file descriptors but changing such call sites (where there is a struct file) could improve API consistency though. Any though? > > Thanks, > Günther > > On Thu, Sep 08, 2022 at 09:58:01PM +0200, Günther Noack wrote: >> Like path_truncate, the file_truncate hook also restricts file >> truncation, but is called in the cases where truncation is attempted >> on an already-opened file. >> >> This is required in a subsequent commit to handle ftruncate() >> operations differently to truncate() operations. >> >> Signed-off-by: Günther Noack >> --- >> fs/namei.c | 6 +++--- >> fs/open.c | 4 ++-- >> include/linux/lsm_hook_defs.h | 1 + >> include/linux/security.h | 6 ++++++ >> security/apparmor/lsm.c | 6 ++++++ >> security/security.c | 5 +++++ >> security/tomoyo/tomoyo.c | 13 +++++++++++++ >> 7 files changed, 36 insertions(+), 5 deletions(-) >> >> diff --git a/fs/namei.c b/fs/namei.c >> index 53b4bc094db2..52105873d1f8 100644 >> --- a/fs/namei.c >> +++ b/fs/namei.c >> @@ -53,8 +53,8 @@ >> * The new code replaces the old recursive symlink resolution with >> * an iterative one (in case of non-nested symlink chains). It does >> * this with calls to _follow_link(). >> - * As a side effect, dir_namei(), _namei() and follow_link() are now >> - * replaced with a single function lookup_dentry() that can handle all >> + * As a side effect, dir_namei(), _namei() and follow_link() are now >> + * replaced with a single function lookup_dentry() that can handle all >> * the special cases of the former code. >> * >> * With the new dcache, the pathname is stored at each inode, at least as >> @@ -3211,7 +3211,7 @@ static int handle_truncate(struct user_namespace *mnt_userns, struct file *filp) >> if (error) >> return error; >> >> - error = security_path_truncate(path); >> + error = security_file_truncate(filp); >> if (!error) { >> error = do_truncate(mnt_userns, path->dentry, 0, >> ATTR_MTIME|ATTR_CTIME|ATTR_OPEN, >> diff --git a/fs/open.c b/fs/open.c >> index 8a813fa5ca56..0831433e493a 100644 >> --- a/fs/open.c >> +++ b/fs/open.c >> @@ -188,7 +188,7 @@ long do_sys_ftruncate(unsigned int fd, loff_t length, int small) >> if (IS_APPEND(file_inode(f.file))) >> goto out_putf; >> sb_start_write(inode->i_sb); >> - error = security_path_truncate(&f.file->f_path); >> + error = security_file_truncate(f.file); >> if (!error) >> error = do_truncate(file_mnt_user_ns(f.file), dentry, length, >> ATTR_MTIME | ATTR_CTIME, f.file); >> @@ -1271,7 +1271,7 @@ struct file *filp_open(const char *filename, int flags, umode_t mode) >> { >> struct filename *name = getname_kernel(filename); >> struct file *file = ERR_CAST(name); >> - >> + >> if (!IS_ERR(name)) { >> file = file_open_name(name, flags, mode); >> putname(name); >> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h >> index 60fff133c0b1..dee35ab253ba 100644 >> --- a/include/linux/lsm_hook_defs.h >> +++ b/include/linux/lsm_hook_defs.h >> @@ -177,6 +177,7 @@ LSM_HOOK(int, 0, file_send_sigiotask, struct task_struct *tsk, >> struct fown_struct *fown, int sig) >> LSM_HOOK(int, 0, file_receive, struct file *file) >> LSM_HOOK(int, 0, file_open, struct file *file) >> +LSM_HOOK(int, 0, file_truncate, struct file *file) >> LSM_HOOK(int, 0, task_alloc, struct task_struct *task, >> unsigned long clone_flags) >> LSM_HOOK(void, LSM_RET_VOID, task_free, struct task_struct *task) >> diff --git a/include/linux/security.h b/include/linux/security.h >> index 7bd0c490703d..f80b23382dd9 100644 >> --- a/include/linux/security.h >> +++ b/include/linux/security.h >> @@ -394,6 +394,7 @@ int security_file_send_sigiotask(struct task_struct *tsk, >> struct fown_struct *fown, int sig); >> int security_file_receive(struct file *file); >> int security_file_open(struct file *file); >> +int security_file_truncate(struct file *file); >> int security_task_alloc(struct task_struct *task, unsigned long clone_flags); >> void security_task_free(struct task_struct *task); >> int security_cred_alloc_blank(struct cred *cred, gfp_t gfp); >> @@ -1011,6 +1012,11 @@ static inline int security_file_open(struct file *file) >> return 0; >> } >> >> +static inline int security_file_truncate(struct file *file) >> +{ >> + return 0; >> +} >> + >> static inline int security_task_alloc(struct task_struct *task, >> unsigned long clone_flags) >> { >> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c >> index e29cade7b662..98ecb7f221b8 100644 >> --- a/security/apparmor/lsm.c >> +++ b/security/apparmor/lsm.c >> @@ -329,6 +329,11 @@ static int apparmor_path_truncate(const struct path *path) >> return common_perm_cond(OP_TRUNC, path, MAY_WRITE | AA_MAY_SETATTR); >> } >> >> +static int apparmor_file_truncate(struct file *file) >> +{ >> + return apparmor_path_truncate(&file->f_path); >> +} >> + >> static int apparmor_path_symlink(const struct path *dir, struct dentry *dentry, >> const char *old_name) >> { >> @@ -1232,6 +1237,7 @@ static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = { >> LSM_HOOK_INIT(mmap_file, apparmor_mmap_file), >> LSM_HOOK_INIT(file_mprotect, apparmor_file_mprotect), >> LSM_HOOK_INIT(file_lock, apparmor_file_lock), >> + LSM_HOOK_INIT(file_truncate, apparmor_file_truncate), >> >> LSM_HOOK_INIT(getprocattr, apparmor_getprocattr), >> LSM_HOOK_INIT(setprocattr, apparmor_setprocattr), >> diff --git a/security/security.c b/security/security.c >> index 4b95de24bc8d..e491120c48ba 100644 >> --- a/security/security.c >> +++ b/security/security.c >> @@ -1210,6 +1210,11 @@ int security_path_truncate(const struct path *path) >> return call_int_hook(path_truncate, 0, path); >> } >> >> +int security_file_truncate(struct file *file) >> +{ >> + return call_int_hook(file_truncate, 0, file); >> +} >> + >> int security_path_chmod(const struct path *path, umode_t mode) >> { >> if (unlikely(IS_PRIVATE(d_backing_inode(path->dentry)))) >> diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c >> index 71e82d855ebf..af04a7b7eb28 100644 >> --- a/security/tomoyo/tomoyo.c >> +++ b/security/tomoyo/tomoyo.c >> @@ -134,6 +134,18 @@ static int tomoyo_path_truncate(const struct path *path) >> return tomoyo_path_perm(TOMOYO_TYPE_TRUNCATE, path, NULL); >> } >> >> +/** >> + * tomoyo_file_truncate - Target for security_file_truncate(). >> + * >> + * @file: Pointer to "struct file". >> + * >> + * Returns 0 on success, negative value otherwise. >> + */ >> +static int tomoyo_file_truncate(struct file *file) >> +{ >> + return tomoyo_path_truncate(&file->f_path); >> +} >> + >> /** >> * tomoyo_path_unlink - Target for security_path_unlink(). >> * >> @@ -545,6 +557,7 @@ static struct security_hook_list tomoyo_hooks[] __lsm_ro_after_init = { >> LSM_HOOK_INIT(bprm_check_security, tomoyo_bprm_check_security), >> LSM_HOOK_INIT(file_fcntl, tomoyo_file_fcntl), >> LSM_HOOK_INIT(file_open, tomoyo_file_open), >> + LSM_HOOK_INIT(file_truncate, tomoyo_file_truncate), >> LSM_HOOK_INIT(path_truncate, tomoyo_path_truncate), >> LSM_HOOK_INIT(path_unlink, tomoyo_path_unlink), >> LSM_HOOK_INIT(path_mkdir, tomoyo_path_mkdir), >> -- >> 2.37.3 >> > > --