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Date: Tue, 14 Jan 2014 12:10:52 -0800
From: John Johansen <john.johansen@...onical.com>
To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
miklos@...redi.hu
CC: mszeredi@...e.cz, linux-security-module@...r.kernel.org,
viro@...iv.linux.org.uk, torvalds@...ux-foundation.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
hch@...radead.org, akpm@...ux-foundation.org, dhowells@...hat.com,
zab@...hat.com, jack@...e.cz, luto@...capital.net
Subject: Re: [PATCH 00/11] cross rename v3
On 01/14/2014 05:03 AM, Tetsuo Handa wrote:
> Miklos Szeredi wrote:
>> On Mon, Jan 13, 2014 at 11:03 PM, Tetsuo Handa
>> <penguin-kernel@...ove.sakura.ne.jp> wrote:
>>> Miklos Szeredi wrote:
>>>> Cross rename (A, B) is equivalent to plain rename(A, B) + plain rename
>>>> (B, A) done as a single atomic operation. If security module allows
>>>> both then cross rename is allowed. If at least one is denied then the
>>>> cross rename is denied.
>>>
>>> Yes, the functionality itself is fine. The problem is how LSM users check
>>> their permissions for the functionality.
>>>
>>>>
>>>> This is prepared for in "[PATCH 06/11] security: add flags to rename
>>>> hooks" and actually done in "[PATCH 07/11] vfs: add cross-rename".
>>>>
>>>> Security people are free to implement a explicit security check for
>>>> cross rename, but I don't think that is in the scope of this patchset.
>>>>
>>> I don't know how their permissions are checked, but I think that
>>> swapping /A/B and /C/D should check not only
>>>
>>> Remove a name from directory A
>>> Add a name to directory C
>>>
>>> but also
>>>
>>> Add a name to directory A
>>> Remove a name from directory C
>>>
>>> using their security labels.
>>>
>>> Without making changes to security/*/ directory, SELinux/SMACK/TOMOYO/AppArmor
>>> might fail to check the latter permissions.
>>
>> Those permissions will be checked. Please see security/security.c in
>> patch 07/11 of the series.
>>
> Oh, I see. But I think that 07/11 is wasteful for security_path_rename() users.
> Why bother to re-calculate /A/B and /C/D using d_absolute_path()?
>
> I prefer flags argument passed to tomoyo_path_rename(). Untested patch follows.
> John, what about AppArmor?
Right policy wise it doesn't make a difference but not having to re-calculate
the paths would be more efficient.
I'd re-factor the apparmor bit of the patch differently so that the paths aren't
recomputed, what is in the patch looks like it should work. In fact I would want
to do the apparmor refactor as a separate patch so that the internal changes
needed to take advantage of the LSM change are separate from the LSM change
it self.
I've only given the patch a quick once over and not tested it yet, but it looks
good, so far.
> ----------
>>>From 4344f31e40b908ab1a6dba9121018d7f37130393 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Tue, 14 Jan 2014 21:55:48 +0900
> Subject: [PATCH] LSM: Pass flags argument to security_path_rename hook users.
>
> Passing flags argument can save TOMOYO from recalculating pathnames
> when cross rename operation is requested.
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> ---
> include/linux/security.h | 4 +++-
> security/apparmor/lsm.c | 17 ++++++++++++++---
> security/capability.c | 3 ++-
> security/security.c | 9 +--------
> security/tomoyo/common.c | 1 +
> security/tomoyo/common.h | 5 ++++-
> security/tomoyo/file.c | 10 +++++++++-
> security/tomoyo/tomoyo.c | 8 ++++++--
> security/tomoyo/util.c | 1 +
> 9 files changed, 41 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 95cfccc..ba8ee7a 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -453,6 +453,7 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
> * @old_dentry contains the dentry structure of the old link.
> * @new_dir contains the path structure for parent of the new link.
> * @new_dentry contains the dentry structure of the new link.
> + * @flags contains rename flags.
> * Return 0 if permission is granted.
> * @path_chmod:
> * Check for permission to change DAC's permission of a file or directory.
> @@ -1491,7 +1492,8 @@ struct security_operations {
> int (*path_link) (struct dentry *old_dentry, struct path *new_dir,
> struct dentry *new_dentry);
> int (*path_rename) (struct path *old_dir, struct dentry *old_dentry,
> - struct path *new_dir, struct dentry *new_dentry);
> + struct path *new_dir, struct dentry *new_dentry,
> + unsigned int flags);
> int (*path_chmod) (struct path *path, umode_t mode);
> int (*path_chown) (struct path *path, kuid_t uid, kgid_t gid);
> int (*path_chroot) (struct path *path);
> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> index 4257b7e..f5d4704 100644
> --- a/security/apparmor/lsm.c
> +++ b/security/apparmor/lsm.c
> @@ -315,7 +315,8 @@ static int apparmor_path_link(struct dentry *old_dentry, struct path *new_dir,
> }
>
> static int apparmor_path_rename(struct path *old_dir, struct dentry *old_dentry,
> - struct path *new_dir, struct dentry *new_dentry)
> + struct path *new_dir, struct dentry *new_dentry,
> + unsigned int flags)
> {
> struct aa_profile *profile;
> int error = 0;
> @@ -330,7 +331,7 @@ static int apparmor_path_rename(struct path *old_dir, struct dentry *old_dentry,
> struct path_cond cond = { old_dentry->d_inode->i_uid,
> old_dentry->d_inode->i_mode
> };
> -
> +retry:
> error = aa_path_perm(OP_RENAME_SRC, profile, &old_path, 0,
> MAY_READ | AA_MAY_META_READ | MAY_WRITE |
> AA_MAY_META_WRITE | AA_MAY_DELETE,
> @@ -339,7 +340,17 @@ static int apparmor_path_rename(struct path *old_dir, struct dentry *old_dentry,
> error = aa_path_perm(OP_RENAME_DEST, profile, &new_path,
> 0, MAY_WRITE | AA_MAY_META_WRITE |
> AA_MAY_CREATE, &cond);
> -
> + if (!error && (flags & RENAME_EXCHANGE)) {
> + /* Cross rename requires both inodes to exist. */
> + old_path.mnt = new_dir->mnt;
> + old_path.dentry = new_dentry;
> + new_path.mnt = old_dir->mnt;
> + new_path.dentry = old_dentry;
> + cond.uid = new_dentry->d_inode->i_uid;
> + cond.mode = new_dentry->d_inode->i_mode;
> + flags = 0;
> + goto retry;
> + }
> }
> return error;
> }
> diff --git a/security/capability.c b/security/capability.c
> index 8b4f24a..cb67fe2 100644
> --- a/security/capability.c
> +++ b/security/capability.c
> @@ -280,7 +280,8 @@ static int cap_path_link(struct dentry *old_dentry, struct path *new_dir,
> }
>
> static int cap_path_rename(struct path *old_path, struct dentry *old_dentry,
> - struct path *new_path, struct dentry *new_dentry)
> + struct path *new_path, struct dentry *new_dentry,
> + unsigned int flags)
> {
> return 0;
> }
> diff --git a/security/security.c b/security/security.c
> index 3dd2258..b14574e 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -440,15 +440,8 @@ int security_path_rename(struct path *old_dir, struct dentry *old_dentry,
> (new_dentry->d_inode && IS_PRIVATE(new_dentry->d_inode))))
> return 0;
>
> - if (flags & RENAME_EXCHANGE) {
> - int err = security_ops->path_rename(new_dir, new_dentry,
> - old_dir, old_dentry);
> - if (err)
> - return err;
> - }
> -
> return security_ops->path_rename(old_dir, old_dentry, new_dir,
> - new_dentry);
> + new_dentry, flags);
> }
> EXPORT_SYMBOL(security_path_rename);
>
> diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
> index 283862a..86747a7 100644
> --- a/security/tomoyo/common.c
> +++ b/security/tomoyo/common.c
> @@ -36,6 +36,7 @@ const char * const tomoyo_mac_keywords[TOMOYO_MAX_MAC_INDEX
> [TOMOYO_MAC_FILE_MKCHAR] = "mkchar",
> [TOMOYO_MAC_FILE_LINK] = "link",
> [TOMOYO_MAC_FILE_RENAME] = "rename",
> + [TOMOYO_MAC_FILE_SWAPNAME] = "swapname",
> [TOMOYO_MAC_FILE_CHMOD] = "chmod",
> [TOMOYO_MAC_FILE_CHOWN] = "chown",
> [TOMOYO_MAC_FILE_CHGRP] = "chgrp",
> diff --git a/security/tomoyo/common.h b/security/tomoyo/common.h
> index b897d48..0349ae9 100644
> --- a/security/tomoyo/common.h
> +++ b/security/tomoyo/common.h
> @@ -276,6 +276,7 @@ enum tomoyo_network_acl_index {
> enum tomoyo_path2_acl_index {
> TOMOYO_TYPE_LINK,
> TOMOYO_TYPE_RENAME,
> + TOMOYO_TYPE_SWAPNAME,
> TOMOYO_TYPE_PIVOT_ROOT,
> TOMOYO_MAX_PATH2_OPERATION
> };
> @@ -335,6 +336,7 @@ enum tomoyo_mac_index {
> TOMOYO_MAC_FILE_MKCHAR,
> TOMOYO_MAC_FILE_LINK,
> TOMOYO_MAC_FILE_RENAME,
> + TOMOYO_MAC_FILE_SWAPNAME,
> TOMOYO_MAC_FILE_CHMOD,
> TOMOYO_MAC_FILE_CHOWN,
> TOMOYO_MAC_FILE_CHGRP,
> @@ -730,7 +732,8 @@ struct tomoyo_mkdev_acl {
> };
>
> /*
> - * Structure for "file rename", "file link" and "file pivot_root" directive.
> + * Structure for "file rename", "file swapname", "file link" and
> + * "file pivot_root" directive.
> */
> struct tomoyo_path2_acl {
> struct tomoyo_acl_info head; /* type = TOMOYO_TYPE_PATH2_ACL */
> diff --git a/security/tomoyo/file.c b/security/tomoyo/file.c
> index 4003907..c7d9546 100644
> --- a/security/tomoyo/file.c
> +++ b/security/tomoyo/file.c
> @@ -38,6 +38,7 @@ const u8 tomoyo_pnnn2mac[TOMOYO_MAX_MKDEV_OPERATION] = {
> const u8 tomoyo_pp2mac[TOMOYO_MAX_PATH2_OPERATION] = {
> [TOMOYO_TYPE_LINK] = TOMOYO_MAC_FILE_LINK,
> [TOMOYO_TYPE_RENAME] = TOMOYO_MAC_FILE_RENAME,
> + [TOMOYO_TYPE_SWAPNAME] = TOMOYO_MAC_FILE_SWAPNAME,
> [TOMOYO_TYPE_PIVOT_ROOT] = TOMOYO_MAC_FILE_PIVOT_ROOT,
> };
>
> @@ -874,7 +875,7 @@ int tomoyo_mkdev_perm(const u8 operation, struct path *path,
> }
>
> /**
> - * tomoyo_path2_perm - Check permission for "rename", "link" and "pivot_root".
> + * tomoyo_path2_perm - Check permission for "rename", "swapname", "link" and "pivot_root".
> *
> * @operation: Type of operation.
> * @path1: Pointer to "struct path".
> @@ -916,6 +917,13 @@ int tomoyo_path2_perm(const u8 operation, struct path *path1,
> tomoyo_add_slash(&buf1);
> tomoyo_add_slash(&buf2);
> break;
> + case TOMOYO_TYPE_SWAPNAME:
> + /* Cross rename requires both inodes to exist. */
> + if (S_ISDIR(path1->dentry->d_inode->i_mode))
> + tomoyo_add_slash(&buf1);
> + if (S_ISDIR(path2->dentry->d_inode->i_mode))
> + tomoyo_add_slash(&buf2);
> + break;
> }
> r.obj = &obj;
> r.param_type = TOMOYO_TYPE_PATH2_ACL;
> diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
> index f0b756e..8e9fb4a 100644
> --- a/security/tomoyo/tomoyo.c
> +++ b/security/tomoyo/tomoyo.c
> @@ -287,17 +287,21 @@ static int tomoyo_path_link(struct dentry *old_dentry, struct path *new_dir,
> * @old_dentry: Pointer to "struct dentry".
> * @new_parent: Pointer to "struct path".
> * @new_dentry: Pointer to "struct dentry".
> + * @flags: Rename flags.
> *
> * Returns 0 on success, negative value otherwise.
> */
> static int tomoyo_path_rename(struct path *old_parent,
> struct dentry *old_dentry,
> struct path *new_parent,
> - struct dentry *new_dentry)
> + struct dentry *new_dentry,
> + unsigned int flags)
> {
> struct path path1 = { old_parent->mnt, old_dentry };
> struct path path2 = { new_parent->mnt, new_dentry };
> - return tomoyo_path2_perm(TOMOYO_TYPE_RENAME, &path1, &path2);
> + return tomoyo_path2_perm((flags & RENAME_EXCHANGE) ?
> + TOMOYO_TYPE_SWAPNAME : TOMOYO_TYPE_RENAME,
> + &path1, &path2);
> }
>
> /**
> diff --git a/security/tomoyo/util.c b/security/tomoyo/util.c
> index 2952ba5..f0ac0be 100644
> --- a/security/tomoyo/util.c
> +++ b/security/tomoyo/util.c
> @@ -34,6 +34,7 @@ const u8 tomoyo_index2category[TOMOYO_MAX_MAC_INDEX] = {
> [TOMOYO_MAC_FILE_MKCHAR] = TOMOYO_MAC_CATEGORY_FILE,
> [TOMOYO_MAC_FILE_LINK] = TOMOYO_MAC_CATEGORY_FILE,
> [TOMOYO_MAC_FILE_RENAME] = TOMOYO_MAC_CATEGORY_FILE,
> + [TOMOYO_MAC_FILE_SWAPNAME] = TOMOYO_MAC_CATEGORY_FILE,
> [TOMOYO_MAC_FILE_CHMOD] = TOMOYO_MAC_CATEGORY_FILE,
> [TOMOYO_MAC_FILE_CHOWN] = TOMOYO_MAC_CATEGORY_FILE,
> [TOMOYO_MAC_FILE_CHGRP] = TOMOYO_MAC_CATEGORY_FILE,
>
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