Messages in this thread | | | Date | Wed, 23 Mar 2022 09:40:35 +0100 | From | Mickaël Salaün <> | Subject | Re: [RFC PATCH v1] LSM: Remove double path_rename hook calls for RENAME_EXCHANGE |
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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
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