From 1e5267cd0895183e09c5bb76da85c674014285d0 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Tue, 21 Jun 2022 16:14:47 +0200 Subject: [PATCH] mnt_idmapping: add vfs{g,u}id_t Introduces new vfs{g,u}id_t types. Similar to k{g,u}id_t the new types are just simple wrapper structs around regular {g,u}id_t types. They allows to establish a type safety boundary between {g,u}ids on idmapped mounts and {g,u}ids as they are represented in filesystems themselves. A vfs{g,u}id_t is always created from a k{g,u}id_t, never directly from a {g,u}id_t as idmapped mounts remap a given {g,u}id according to the mount's idmapping. This is expressed in the VFS{G,U}IDT_INIT() macros. A vfs{g,u}id_t may be used as a k{g,u}id_t via AS_K{G,U}IDT(). This often happens when we need to check whether a {g,u}id mapped according to an idmapped mount is identical to a given k{g,u}id_t. For an example, see vfsgid_in_group_p() which determines whether the value of vfsgid_t matches the value of any of the caller's groups. Similar logic is expressed in the k{g,u}id_eq_vfs{g,u}id(). The from_vfs{g,u}id() helpers map a given vfs{g,u}id_t from the mount's idmapping into the filesystem idmapping. They make it possible to update a filesystem object such as inode->i_{g,u}id with the correct value. This makes it harder to accidently write a wrong {g,u}id anwywhere. The vfs{g,u}id_has_fsmapping() helpers check whether a given vfs{g,u}id_t can be mapped into the filesystem idmapping. All new helpers are nops on non-idmapped mounts. I've done work on this roughly 7 months ago but dropped it to focus on the testsuite. Linus brought this up independently just last week and it's time to move this along (see [1]). [1]: https://lore.kernel.org/lkml/CAHk-=win6+ahs1EwLkcq8apqLi_1wXFWbrPf340zYEhObpz4jA@mail.gmail.com Link: https://lore.kernel.org/r/20220621141454.2914719-2-brauner@kernel.org Cc: Seth Forshee Cc: Christoph Hellwig Cc: Aleksa Sarai Cc: Linus Torvalds Cc: Al Viro CC: linux-fsdevel@vger.kernel.org Reviewed-by: Seth Forshee Signed-off-by: Christian Brauner (Microsoft) --- include/linux/mnt_idmapping.h | 262 ++++++++++++++++++++++++++++++---- 1 file changed, 234 insertions(+), 28 deletions(-) diff --git a/include/linux/mnt_idmapping.h b/include/linux/mnt_idmapping.h index ee5a217de2a8..71b4cd5a7466 100644 --- a/include/linux/mnt_idmapping.h +++ b/include/linux/mnt_idmapping.h @@ -13,6 +13,122 @@ struct user_namespace; */ extern struct user_namespace init_user_ns; +typedef struct { + uid_t val; +} vfsuid_t; + +typedef struct { + gid_t val; +} vfsgid_t; + +#ifdef CONFIG_MULTIUSER +static inline uid_t __vfsuid_val(vfsuid_t uid) +{ + return uid.val; +} + +static inline gid_t __vfsgid_val(vfsgid_t gid) +{ + return gid.val; +} +#else +static inline uid_t __vfsuid_val(vfsuid_t uid) +{ + return 0; +} + +static inline gid_t __vfsgid_val(vfsgid_t gid) +{ + return 0; +} +#endif + +static inline bool vfsuid_valid(vfsuid_t uid) +{ + return __vfsuid_val(uid) != (uid_t)-1; +} + +static inline bool vfsgid_valid(vfsgid_t gid) +{ + return __vfsgid_val(gid) != (gid_t)-1; +} + +static inline bool vfsuid_eq(vfsuid_t left, vfsuid_t right) +{ + return __vfsuid_val(left) == __vfsuid_val(right); +} + +static inline bool vfsgid_eq(vfsgid_t left, vfsgid_t right) +{ + return __vfsgid_val(left) == __vfsgid_val(right); +} + +/** + * vfsuid_eq_kuid - check whether kuid and vfsuid have the same value + * @kuid: the kuid to compare + * @vfsuid: the vfsuid to compare + * + * Check whether @kuid and @vfsuid have the same values. + * + * Return: true if @kuid and @vfsuid have the same value, false if not. + */ +static inline bool vfsuid_eq_kuid(vfsuid_t vfsuid, kuid_t kuid) +{ + return __vfsuid_val(vfsuid) == __kuid_val(kuid); +} + +/** + * vfsgid_eq_kgid - check whether kgid and vfsgid have the same value + * @kgid: the kgid to compare + * @vfsgid: the vfsgid to compare + * + * Check whether @kgid and @vfsgid have the same values. + * + * Return: true if @kgid and @vfsgid have the same value, false if not. + */ +static inline bool vfsgid_eq_kgid(kgid_t kgid, vfsgid_t vfsgid) +{ + return __vfsgid_val(vfsgid) == __kgid_val(kgid); +} + +/* + * vfs{g,u}ids are created from k{g,u}ids. + * We don't allow them to be created from regular {u,g}id. + */ +#define VFSUIDT_INIT(val) (vfsuid_t){ __kuid_val(val) } +#define VFSGIDT_INIT(val) (vfsgid_t){ __kgid_val(val) } + +#define INVALID_VFSUID VFSUIDT_INIT(INVALID_UID) +#define INVALID_VFSGID VFSGIDT_INIT(INVALID_GID) + +/* + * Allow a vfs{g,u}id to be used as a k{g,u}id where we want to compare + * whether the mapped value is identical to value of a k{g,u}id. + */ +#define AS_KUIDT(val) (kuid_t){ __vfsuid_val(val) } +#define AS_KGIDT(val) (kgid_t){ __vfsgid_val(val) } + +#ifdef CONFIG_MULTIUSER +/** + * vfsgid_in_group_p() - check whether a vfsuid matches the caller's groups + * @vfsgid: the mnt gid to match + * + * This function can be used to determine whether @vfsuid matches any of the + * caller's groups. + * + * Return: 1 if vfsuid matches caller's groups, 0 if not. + */ +static inline int vfsgid_in_group_p(vfsgid_t vfsgid) +{ + return in_group_p(AS_KGIDT(vfsgid)); +} +#else +static inline int vfsgid_in_group_p(vfsgid_t vfsgid) +{ + return 1; +} +#endif + /** * initial_idmapping - check whether this is the initial mapping * @ns: idmapping to check @@ -67,21 +183,29 @@ static inline bool no_idmapping(const struct user_namespace *mnt_userns, * If @kuid has no mapping in either @mnt_userns or @fs_userns INVALID_UID is * returned. */ -static inline kuid_t mapped_kuid_fs(struct user_namespace *mnt_userns, - struct user_namespace *fs_userns, - kuid_t kuid) + +static inline vfsuid_t make_vfsuid(struct user_namespace *mnt_userns, + struct user_namespace *fs_userns, + kuid_t kuid) { uid_t uid; if (no_idmapping(mnt_userns, fs_userns)) - return kuid; + return VFSUIDT_INIT(kuid); if (initial_idmapping(fs_userns)) uid = __kuid_val(kuid); else uid = from_kuid(fs_userns, kuid); if (uid == (uid_t)-1) - return INVALID_UID; - return make_kuid(mnt_userns, uid); + return INVALID_VFSUID; + return VFSUIDT_INIT(make_kuid(mnt_userns, uid)); +} + +static inline kuid_t mapped_kuid_fs(struct user_namespace *mnt_userns, + struct user_namespace *fs_userns, + kuid_t kuid) +{ + return AS_KUIDT(make_vfsuid(mnt_userns, fs_userns, kuid)); } /** @@ -104,21 +228,56 @@ static inline kuid_t mapped_kuid_fs(struct user_namespace *mnt_userns, * If @kgid has no mapping in either @mnt_userns or @fs_userns INVALID_GID is * returned. */ -static inline kgid_t mapped_kgid_fs(struct user_namespace *mnt_userns, - struct user_namespace *fs_userns, - kgid_t kgid) + +static inline vfsgid_t make_vfsgid(struct user_namespace *mnt_userns, + struct user_namespace *fs_userns, + kgid_t kgid) { gid_t gid; if (no_idmapping(mnt_userns, fs_userns)) - return kgid; + return VFSGIDT_INIT(kgid); if (initial_idmapping(fs_userns)) gid = __kgid_val(kgid); else gid = from_kgid(fs_userns, kgid); if (gid == (gid_t)-1) - return INVALID_GID; - return make_kgid(mnt_userns, gid); + return INVALID_VFSGID; + return VFSGIDT_INIT(make_kgid(mnt_userns, gid)); +} + +static inline kgid_t mapped_kgid_fs(struct user_namespace *mnt_userns, + struct user_namespace *fs_userns, + kgid_t kgid) +{ + return AS_KGIDT(make_vfsgid(mnt_userns, fs_userns, kgid)); +} + +/** + * from_vfsuid - map a vfsuid into the filesystem idmapping + * @mnt_userns: the mount's idmapping + * @fs_userns: the filesystem's idmapping + * @vfsuid : vfsuid to be mapped + * + * Map @vfsuid into the filesystem idmapping. This function has to be used in + * order to e.g. write @vfsuid to inode->i_uid. + * + * Return: @vfsuid mapped into the filesystem idmapping + */ +static inline kuid_t from_vfsuid(struct user_namespace *mnt_userns, + struct user_namespace *fs_userns, + vfsuid_t vfsuid) +{ + uid_t uid; + + if (no_idmapping(mnt_userns, fs_userns)) + return AS_KUIDT(vfsuid); + uid = from_kuid(mnt_userns, AS_KUIDT(vfsuid)); + if (uid == (uid_t)-1) + return INVALID_UID; + if (initial_idmapping(fs_userns)) + return KUIDT_INIT(uid); + return make_kuid(fs_userns, uid); } /** @@ -145,16 +304,53 @@ static inline kuid_t mapped_kuid_user(struct user_namespace *mnt_userns, struct user_namespace *fs_userns, kuid_t kuid) { - uid_t uid; + return from_vfsuid(mnt_userns, fs_userns, VFSUIDT_INIT(kuid)); +} + +/** + * vfsuid_has_fsmapping - check whether a vfsuid maps into the filesystem + * @mnt_userns: the mount's idmapping + * @fs_userns: the filesystem's idmapping + * @vfsuid: vfsuid to be mapped + * + * Check whether @vfsuid has a mapping in the filesystem idmapping. Use this + * function to check whether the filesystem idmapping has a mapping for + * @vfsuid. + * + * Return: true if @vfsuid has a mapping in the filesystem, false if not. + */ +static inline bool vfsuid_has_fsmapping(struct user_namespace *mnt_userns, + struct user_namespace *fs_userns, + vfsuid_t vfsuid) +{ + return uid_valid(from_vfsuid(mnt_userns, fs_userns, vfsuid)); +} + +/** + * from_vfsgid - map a vfsgid into the filesystem idmapping + * @mnt_userns: the mount's idmapping + * @fs_userns: the filesystem's idmapping + * @vfsgid : vfsgid to be mapped + * + * Map @vfsgid into the filesystem idmapping. This function has to be used in + * order to e.g. write @vfsgid to inode->i_gid. + * + * Return: @vfsgid mapped into the filesystem idmapping + */ +static inline kgid_t from_vfsgid(struct user_namespace *mnt_userns, + struct user_namespace *fs_userns, + vfsgid_t vfsgid) +{ + gid_t gid; if (no_idmapping(mnt_userns, fs_userns)) - return kuid; - uid = from_kuid(mnt_userns, kuid); - if (uid == (uid_t)-1) - return INVALID_UID; + return AS_KGIDT(vfsgid); + gid = from_kgid(mnt_userns, AS_KGIDT(vfsgid)); + if (gid == (gid_t)-1) + return INVALID_GID; if (initial_idmapping(fs_userns)) - return KUIDT_INIT(uid); - return make_kuid(fs_userns, uid); + return KGIDT_INIT(gid); + return make_kgid(fs_userns, gid); } /** @@ -181,16 +377,26 @@ static inline kgid_t mapped_kgid_user(struct user_namespace *mnt_userns, struct user_namespace *fs_userns, kgid_t kgid) { - gid_t gid; + return from_vfsgid(mnt_userns, fs_userns, VFSGIDT_INIT(kgid)); +} - if (no_idmapping(mnt_userns, fs_userns)) - return kgid; - gid = from_kgid(mnt_userns, kgid); - if (gid == (gid_t)-1) - return INVALID_GID; - if (initial_idmapping(fs_userns)) - return KGIDT_INIT(gid); - return make_kgid(fs_userns, gid); +/** + * vfsgid_has_fsmapping - check whether a vfsgid maps into the filesystem + * @mnt_userns: the mount's idmapping + * @fs_userns: the filesystem's idmapping + * @vfsgid: vfsgid to be mapped + * + * Check whether @vfsgid has a mapping in the filesystem idmapping. Use this + * function to check whether the filesystem idmapping has a mapping for + * @vfsgid. + * + * Return: true if @vfsgid has a mapping in the filesystem, false if not. + */ +static inline bool vfsgid_has_fsmapping(struct user_namespace *mnt_userns, + struct user_namespace *fs_userns, + vfsgid_t vfsgid) +{ + return gid_valid(from_vfsgid(mnt_userns, fs_userns, vfsgid)); } /**