Messages in this thread | | | Date | Wed, 23 Mar 2022 23:36:58 +0100 | From | Mickaël Salaün <> | Subject | Re: [RFC PATCH v1] LSM: Remove double path_rename hook calls for RENAME_EXCHANGE |
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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 >
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