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Message-ID: <b71454bb-d084-bfd6-7cd3-aa6bfdaaab00@digikod.net>
Date: Wed, 23 Mar 2022 09:40:35 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: James Morris <jmorris@...ei.org>,
John Johansen <john.johansen@...onical.com>,
Kentaro Takeda <takedakn@...data.co.jp>,
"Serge E . Hallyn" <serge@...lyn.com>,
Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: Brendan Jackman <jackmanb@...omium.org>,
Florent Revest <revest@...omium.org>,
KP Singh <kpsingh@...nel.org>,
Paul Moore <paul@...l-moore.com>, linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org,
Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [RFC PATCH v1] LSM: Remove double path_rename hook calls for
RENAME_EXCHANGE
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@...ux.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@...ei.org>
> Cc: John Johansen <john.johansen@...onical.com>
> Cc: Kentaro Takeda <takedakn@...data.co.jp>
> Cc: Serge E. Hallyn <serge@...lyn.com>
> Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Signed-off-by: Mickaël Salaün <mic@...ux.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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