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acl: move idmapping handling into posix_acl_xattr_set()
The uapi POSIX ACL struct passed through the value argument during
setxattr() contains {g,u}id values encoded via ACL_{GROUP,USER} entries
that should actually be stored in the form of k{g,u}id_t (See [1] for a
long explanation of the issue.).
In 0c5fd887d2
("acl: move idmapped mount fixup into vfs_{g,s}etxattr()")
we took the mount's idmapping into account in order to let overlayfs
handle POSIX ACLs on idmapped layers correctly. The fixup is currently
performed directly in vfs_setxattr() which piles on top of the earlier
hackiness by handling the mount's idmapping and stuff the vfs{g,u}id_t
values into the uapi struct as well. While that is all correct and works
fine it's just ugly.
Now that we have introduced vfs_make_posix_acl() earlier move handling
idmapped mounts out of vfs_setxattr() and into the POSIX ACL handler
where it belongs.
Note that we also need to call vfs_make_posix_acl() for EVM which
interpretes POSIX ACLs during security_inode_setxattr(). Leave them a
longer comment for future reference.
All filesystems that support idmapped mounts via FS_ALLOW_IDMAP use the
standard POSIX ACL xattr handlers and are covered by this change. This
includes overlayfs which simply calls vfs_{g,s}etxattr().
The following filesystems use custom POSIX ACL xattr handlers: 9p, cifs,
ecryptfs, and ntfs3 (and overlayfs but we've covered that in the paragraph
above) and none of them support idmapped mounts yet.
Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org/ [1]
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Reviewed-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
This commit is contained in:
parent
6b70fe0601
commit
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@ -771,46 +771,6 @@ void posix_acl_getxattr_idmapped_mnt(struct user_namespace *mnt_userns,
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}
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}
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void posix_acl_setxattr_idmapped_mnt(struct user_namespace *mnt_userns,
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const struct inode *inode,
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void *value, size_t size)
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{
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struct posix_acl_xattr_header *header = value;
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struct posix_acl_xattr_entry *entry = (void *)(header + 1), *end;
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struct user_namespace *fs_userns = i_user_ns(inode);
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int count;
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vfsuid_t vfsuid;
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vfsgid_t vfsgid;
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kuid_t uid;
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kgid_t gid;
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if (no_idmapping(mnt_userns, i_user_ns(inode)))
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return;
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count = posix_acl_fix_xattr_common(value, size);
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if (count <= 0)
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return;
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for (end = entry + count; entry != end; entry++) {
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switch (le16_to_cpu(entry->e_tag)) {
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case ACL_USER:
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uid = make_kuid(&init_user_ns, le32_to_cpu(entry->e_id));
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vfsuid = VFSUIDT_INIT(uid);
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uid = from_vfsuid(mnt_userns, fs_userns, vfsuid);
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entry->e_id = cpu_to_le32(from_kuid(&init_user_ns, uid));
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break;
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case ACL_GROUP:
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gid = make_kgid(&init_user_ns, le32_to_cpu(entry->e_id));
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vfsgid = VFSGIDT_INIT(gid);
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gid = from_vfsgid(mnt_userns, fs_userns, vfsgid);
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entry->e_id = cpu_to_le32(from_kgid(&init_user_ns, gid));
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break;
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default:
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break;
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}
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}
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}
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static void posix_acl_fix_xattr_userns(
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struct user_namespace *to, struct user_namespace *from,
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void *value, size_t size)
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@ -1211,7 +1171,17 @@ posix_acl_xattr_set(const struct xattr_handler *handler,
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int ret;
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if (value) {
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acl = posix_acl_from_xattr(&init_user_ns, value, size);
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/*
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* By the time we end up here the {g,u}ids stored in
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* ACL_{GROUP,USER} have already been mapped according to the
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* caller's idmapping. The vfs_set_acl_prepare() helper will
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* recover them and take idmapped mounts into account. The
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* filesystem will receive the POSIX ACLs in in the correct
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* format ready to be cached or written to the backing store
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* taking the filesystem idmapping into account.
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*/
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acl = vfs_set_acl_prepare(mnt_userns, i_user_ns(inode),
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value, size);
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if (IS_ERR(acl))
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return PTR_ERR(acl);
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}
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@ -305,9 +305,6 @@ vfs_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
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size = error;
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}
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if (size && is_posix_acl_xattr(name))
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posix_acl_setxattr_idmapped_mnt(mnt_userns, inode, value, size);
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retry_deleg:
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inode_lock(inode);
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error = __vfs_setxattr_locked(mnt_userns, dentry, name, value, size,
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@ -38,9 +38,6 @@ void posix_acl_fix_xattr_to_user(void *value, size_t size);
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void posix_acl_getxattr_idmapped_mnt(struct user_namespace *mnt_userns,
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const struct inode *inode,
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void *value, size_t size);
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void posix_acl_setxattr_idmapped_mnt(struct user_namespace *mnt_userns,
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const struct inode *inode,
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void *value, size_t size);
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#else
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static inline void posix_acl_fix_xattr_from_user(void *value, size_t size)
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{
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@ -54,12 +51,6 @@ posix_acl_getxattr_idmapped_mnt(struct user_namespace *mnt_userns,
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size_t size)
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{
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}
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static inline void
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posix_acl_setxattr_idmapped_mnt(struct user_namespace *mnt_userns,
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const struct inode *inode, void *value,
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size_t size)
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{
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}
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#endif
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struct posix_acl *posix_acl_from_xattr(struct user_namespace *user_ns,
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@ -457,10 +457,21 @@ static int evm_xattr_acl_change(struct user_namespace *mnt_userns,
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int rc;
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/*
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* user_ns is not relevant here, ACL_USER/ACL_GROUP don't have impact
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* on the inode mode (see posix_acl_equiv_mode()).
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* An earlier comment here mentioned that the idmappings for
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* ACL_{GROUP,USER} don't matter since EVM is only interested in the
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* mode stored as part of POSIX ACLs. Nonetheless, if it must translate
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* from the uapi POSIX ACL representation to the VFS internal POSIX ACL
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* representation it should do so correctly. There's no guarantee that
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* we won't change POSIX ACLs in a way that ACL_{GROUP,USER} matters
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* for the mode at some point and it's difficult to keep track of all
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* the LSM and integrity modules and what they do to POSIX ACLs.
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*
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* Frankly, EVM shouldn't try to interpret the uapi struct for POSIX
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* ACLs it received. It requires knowledge that only the VFS is
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* guaranteed to have.
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*/
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acl = posix_acl_from_xattr(&init_user_ns, xattr_value, xattr_value_len);
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acl = vfs_set_acl_prepare(mnt_userns, i_user_ns(inode),
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xattr_value, xattr_value_len);
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if (IS_ERR_OR_NULL(acl))
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return 1;
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