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Message-ID: <56ae0002-09ed-55ae-d033-0212fe78002c@digikod.net>
Date:   Wed, 23 Mar 2022 23:36:58 +0100
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To:     John Johansen <john.johansen@canonical.com>,
        James Morris <jmorris@namei.org>,
        Kentaro Takeda <takedakn@nttdata.co.jp>,
        "Serge E . Hallyn" <serge@hallyn.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc:     Brendan Jackman <jackmanb@chromium.org>,
        Florent Revest <revest@chromium.org>,
        KP Singh <kpsingh@kernel.org>,
        Paul Moore <paul@paul-moore.com>, linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= <mic@linux.microsoft.com>
References: <20220222175332.384545-1-mic@digikod.net>
 <b71454bb-d084-bfd6-7cd3-aa6bfdaaab00@digikod.net>
 <4611f869-9a88-12d0-861c-7efcfa15bcba@canonical.com>
From:   =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= <mic@digikod.net>
Subject: Re: [RFC PATCH v1] LSM: Remove double path_rename hook calls for
 RENAME_EXCHANGE
In-Reply-To: <4611f869-9a88-12d0-861c-7efcfa15bcba@canonical.com>
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Thanks Tetsuo and John. I'll include this patch in the rename/link 
Landlock series to fix the remaining issue: 
https://lore.kernel.org/r/20220221212522.320243-1-mic@digikod.net


On 23/03/2022 18:38, John Johansen wrote:
> Looks good to me. Of course now I am going to have to create a follow-up
> patch to optimize the apparmor mediation.
> 
> Acked-by: John Johansen <john.johansen@canonical.com>
> 
> On 3/23/22 01:40, Mickaël Salaün wrote:
>> Any comment? John, Tetsuo, does it look OK for AppArmor and Tomoyo?
>>
>> On 22/02/2022 18:53, Mickaël Salaün wrote:
>>> From: Mickaël Salaün <mic@linux.microsoft.com>
>>>
>>> In order to be able to identify a file exchange with renameat2(2) and
>>> RENAME_EXCHANGE, which will be useful for Landlock [1], propagate the
>>> rename flags to LSMs.  This may also improve performance because of the
>>> switch from two set of LSM hook calls to only one, and because LSMs
>>> using this hook may optimize the double check (e.g. only one lock,
>>> reduce the number of path walks).
>>>
>>> AppArmor, Landlock and Tomoyo are updated to leverage this change.  This
>>> should not change the current behavior (same check order), except
>>> (different level of) speed boosts.
>>>
>>> [1] https://lore.kernel.org/r/20220221212522.320243-1-mic@digikod.net
>>>
>>> Cc: James Morris <jmorris@namei.org>
>>> Cc: John Johansen <john.johansen@canonical.com>
>>> Cc: Kentaro Takeda <takedakn@nttdata.co.jp>
>>> Cc: Serge E. Hallyn <serge@hallyn.com>
>>> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>>> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
>>> Link: https://lore.kernel.org/r/20220222175332.384545-1-mic@digikod.net
>>> ---
>>>    include/linux/lsm_hook_defs.h |  2 +-
>>>    include/linux/lsm_hooks.h     |  1 +
>>>    security/apparmor/lsm.c       | 30 +++++++++++++++++++++++++-----
>>>    security/landlock/fs.c        | 12 ++++++++++--
>>>    security/security.c           |  9 +--------
>>>    security/tomoyo/tomoyo.c      | 11 ++++++++++-
>>>    6 files changed, 48 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
>>> index 819ec92dc2a8..d8b49c9c3a8a 100644
>>> --- a/include/linux/lsm_hook_defs.h
>>> +++ b/include/linux/lsm_hook_defs.h
>>> @@ -100,7 +100,7 @@ LSM_HOOK(int, 0, path_link, struct dentry *old_dentry,
>>>         const struct path *new_dir, struct dentry *new_dentry)
>>>    LSM_HOOK(int, 0, path_rename, const struct path *old_dir,
>>>         struct dentry *old_dentry, const struct path *new_dir,
>>> -     struct dentry *new_dentry)
>>> +     struct dentry *new_dentry, unsigned int flags)
>>>    LSM_HOOK(int, 0, path_chmod, const struct path *path, umode_t mode)
>>>    LSM_HOOK(int, 0, path_chown, const struct path *path, kuid_t uid, kgid_t gid)
>>>    LSM_HOOK(int, 0, path_chroot, const struct path *path)
>>> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
>>> index 3bf5c658bc44..32cd2a7fe9fc 100644
>>> --- a/include/linux/lsm_hooks.h
>>> +++ b/include/linux/lsm_hooks.h
>>> @@ -358,6 +358,7 @@
>>>     *    @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 may contain rename options such as RENAME_EXCHANGE.
>>>     *    Return 0 if permission is granted.
>>>     * @path_chmod:
>>>     *    Check for permission to change a mode of the file @path. The new
>>> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
>>> index 4f0eecb67dde..900bc540656a 100644
>>> --- a/security/apparmor/lsm.c
>>> +++ b/security/apparmor/lsm.c
>>> @@ -354,13 +354,16 @@ static int apparmor_path_link(struct dentry *old_dentry, const struct path *new_
>>>    }
>>>      static int apparmor_path_rename(const struct path *old_dir, struct dentry *old_dentry,
>>> -                const struct path *new_dir, struct dentry *new_dentry)
>>> +                const struct path *new_dir, struct dentry *new_dentry,
>>> +                const unsigned int flags)
>>>    {
>>>        struct aa_label *label;
>>>        int error = 0;
>>>          if (!path_mediated_fs(old_dentry))
>>>            return 0;
>>> +    if ((flags & RENAME_EXCHANGE) && !path_mediated_fs(new_dentry))
>>> +        return 0;
>>>          label = begin_current_label_crit_section();
>>>        if (!unconfined(label)) {
>>> @@ -374,10 +377,27 @@ static int apparmor_path_rename(const struct path *old_dir, struct dentry *old_d
>>>                d_backing_inode(old_dentry)->i_mode
>>>            };
>>>    -        error = aa_path_perm(OP_RENAME_SRC, label, &old_path, 0,
>>> -                     MAY_READ | AA_MAY_GETATTR | MAY_WRITE |
>>> -                     AA_MAY_SETATTR | AA_MAY_DELETE,
>>> -                     &cond);
>>> +        if (flags & RENAME_EXCHANGE) {
>>> +            struct path_cond cond_exchange = {
>>> +                i_uid_into_mnt(mnt_userns, d_backing_inode(new_dentry)),
>>> +                d_backing_inode(new_dentry)->i_mode
>>> +            };
>>> +
>>> +            error = aa_path_perm(OP_RENAME_SRC, label, &new_path, 0,
>>> +                         MAY_READ | AA_MAY_GETATTR | MAY_WRITE |
>>> +                         AA_MAY_SETATTR | AA_MAY_DELETE,
>>> +                         &cond_exchange);
>>> +            if (!error)
>>> +                error = aa_path_perm(OP_RENAME_DEST, label, &old_path,
>>> +                             0, MAY_WRITE | AA_MAY_SETATTR |
>>> +                             AA_MAY_CREATE, &cond_exchange);
>>> +        }
>>> +
>>> +        if (!error)
>>> +            error = aa_path_perm(OP_RENAME_SRC, label, &old_path, 0,
>>> +                         MAY_READ | AA_MAY_GETATTR | MAY_WRITE |
>>> +                         AA_MAY_SETATTR | AA_MAY_DELETE,
>>> +                         &cond);
>>>            if (!error)
>>>                error = aa_path_perm(OP_RENAME_DEST, label, &new_path,
>>>                             0, MAY_WRITE | AA_MAY_SETATTR |
>>> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
>>> index 97b8e421f617..7e57fca6e814 100644
>>> --- a/security/landlock/fs.c
>>> +++ b/security/landlock/fs.c
>>> @@ -574,10 +574,12 @@ static inline u32 maybe_remove(const struct dentry *const dentry)
>>>    static int hook_path_rename(const struct path *const old_dir,
>>>            struct dentry *const old_dentry,
>>>            const struct path *const new_dir,
>>> -        struct dentry *const new_dentry)
>>> +        struct dentry *const new_dentry,
>>> +        const unsigned int flags)
>>>    {
>>>        const struct landlock_ruleset *const dom =
>>>            landlock_get_current_domain();
>>> +    u32 exchange_access = 0;
>>>          if (!dom)
>>>            return 0;
>>> @@ -585,11 +587,17 @@ static int hook_path_rename(const struct path *const old_dir,
>>>        if (old_dir->dentry != new_dir->dentry)
>>>            /* Gracefully forbids reparenting. */
>>>            return -EXDEV;
>>> +    if (flags & RENAME_EXCHANGE) {
>>> +        if (unlikely(d_is_negative(new_dentry)))
>>> +            return -ENOENT;
>>> +        exchange_access =
>>> +            get_mode_access(d_backing_inode(new_dentry)->i_mode);
>>> +    }
>>>        if (unlikely(d_is_negative(old_dentry)))
>>>            return -ENOENT;
>>>        /* RENAME_EXCHANGE is handled because directories are the same. */
>>>        return check_access_path(dom, old_dir, maybe_remove(old_dentry) |
>>> -            maybe_remove(new_dentry) |
>>> +            maybe_remove(new_dentry) | exchange_access |
>>>                get_mode_access(d_backing_inode(old_dentry)->i_mode));
>>>    }
>>>    diff --git a/security/security.c b/security/security.c
>>> index 22261d79f333..8634da4cfd46 100644
>>> --- a/security/security.c
>>> +++ b/security/security.c
>>> @@ -1184,15 +1184,8 @@ int security_path_rename(const struct path *old_dir, struct dentry *old_dentry,
>>>                 (d_is_positive(new_dentry) && IS_PRIVATE(d_backing_inode(new_dentry)))))
>>>            return 0;
>>>    -    if (flags & RENAME_EXCHANGE) {
>>> -        int err = call_int_hook(path_rename, 0, new_dir, new_dentry,
>>> -                    old_dir, old_dentry);
>>> -        if (err)
>>> -            return err;
>>> -    }
>>> -
>>>        return call_int_hook(path_rename, 0, old_dir, old_dentry, new_dir,
>>> -                new_dentry);
>>> +                new_dentry, flags);
>>>    }
>>>    EXPORT_SYMBOL(security_path_rename);
>>>    diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
>>> index b6a31901f289..71e82d855ebf 100644
>>> --- a/security/tomoyo/tomoyo.c
>>> +++ b/security/tomoyo/tomoyo.c
>>> @@ -264,17 +264,26 @@ static int tomoyo_path_link(struct dentry *old_dentry, const struct path *new_di
>>>     * @old_dentry: Pointer to "struct dentry".
>>>     * @new_parent: Pointer to "struct path".
>>>     * @new_dentry: Pointer to "struct dentry".
>>> + * @flags: Rename options.
>>>     *
>>>     * Returns 0 on success, negative value otherwise.
>>>     */
>>>    static int tomoyo_path_rename(const struct path *old_parent,
>>>                      struct dentry *old_dentry,
>>>                      const struct path *new_parent,
>>> -                  struct dentry *new_dentry)
>>> +                  struct dentry *new_dentry,
>>> +                  const unsigned int flags)
>>>    {
>>>        struct path path1 = { .mnt = old_parent->mnt, .dentry = old_dentry };
>>>        struct path path2 = { .mnt = new_parent->mnt, .dentry = new_dentry };
>>>    +    if (flags & RENAME_EXCHANGE) {
>>> +        const int err = tomoyo_path2_perm(TOMOYO_TYPE_RENAME, &path2,
>>> +                &path1);
>>> +
>>> +        if (err)
>>> +            return err;
>>> +    }
>>>        return tomoyo_path2_perm(TOMOYO_TYPE_RENAME, &path1, &path2);
>>>    }
>>>   
>>> base-commit: cfb92440ee71adcc2105b0890bb01ac3cddb8507
>