[RFC PATCH v1] LSM: Remove double path_rename hook calls for RENAME_EXCHANGE
Mickaël Salaün
mic at digikod.net
Wed Mar 23 22:36:58 UTC 2022
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 at 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 at 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 at namei.org>
>>> Cc: John Johansen <john.johansen at canonical.com>
>>> Cc: Kentaro Takeda <takedakn at nttdata.co.jp>
>>> Cc: Serge E. Hallyn <serge at hallyn.com>
>>> Cc: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
>>> Signed-off-by: Mickaël Salaün <mic at 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
>
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