From 100f59d964050020285f0c8264ce520f0c406c13 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Micka=C3=ABl=20Sala=C3=BCn?= Date: Fri, 6 May 2022 18:10:56 +0200 Subject: [PATCH] LSM: Remove double path_rename hook calls for RENAME_EXCHANGE MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Cc: Kentaro Takeda Cc: Serge E. Hallyn Acked-by: John Johansen Acked-by: Tetsuo Handa Reviewed-by: Paul Moore Signed-off-by: Mickaël Salaün Link: https://lore.kernel.org/r/20220506161102.525323-7-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 | 11 ++++++++++- security/security.c | 9 +-------- security/tomoyo/tomoyo.c | 11 ++++++++++- 6 files changed, 48 insertions(+), 16 deletions(-) diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index db924fe..eafa1d24 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 419b5fe..9acf5e3 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 4f0eecb..900bc54 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 7b78600..30b42cd 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -622,10 +622,12 @@ static int hook_path_link(struct dentry *const old_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; @@ -633,12 +635,19 @@ 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) | + exchange_access | get_mode_access(d_backing_inode(old_dentry)->i_mode)); } diff --git a/security/security.c b/security/security.c index b7cf5cb..c9bfc0b 100644 --- a/security/security.c +++ b/security/security.c @@ -1197,15 +1197,8 @@ 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 b6a3190..71e82d8 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); } -- 2.7.4