[PATCH v3 13/21] fs: Update posix_acl support to handle user namespace mounts

Seth Forshee
2016-04-22T15:39:45Z

ids in on-disk ACLs should be converted to s_user_ns instead of
init_user_ns as is done now. This introduces the possibility for
id mappings to fail, and when this happens syscalls will return
EOVERFLOW.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
---
fs/posix_acl.c | 67 ++++++++++++++++++++++++++---------------
fs/xattr.c | 19 +++++++++---
include/linux/posix_acl_xattr.h | 17 ++++++++---
3 files changed, 70 insertions(+), 33 deletions(-)

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 711dd5170376..dac2842dd4cb 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -595,59 +595,77 @@ EXPORT_SYMBOL_GPL(posix_acl_create);
/*
* Fix up the uids and gids in posix acl extended attributes in place.
*/
-static void posix_acl_fix_xattr_userns(
+static int posix_acl_fix_xattr_userns(
struct user_namespace *to, struct user_namespace *from,
void *value, size_t size)
{
posix_acl_xattr_header *header = (posix_acl_xattr_header *)value;
posix_acl_xattr_entry *entry = (posix_acl_xattr_entry *)(header+1), *end;
int count;
- kuid_t uid;
- kgid_t gid;
+ kuid_t kuid;
+ uid_t uid;
+ kgid_t kgid;
+ gid_t gid;

if (!value)
- return;
+ return 0;
if (size < sizeof(posix_acl_xattr_header))
- return;
+ return 0;
if (header->a_version != cpu_to_le32(POSIX_ACL_XATTR_VERSION))
- return;
+ return 0;

count = posix_acl_xattr_count(size);
if (count < 0)
- return;
+ return 0;
if (count == 0)
- return;
+ return 0;

for (end = entry + count; entry != end; entry++) {
switch(le16_to_cpu(entry->e_tag)) {
case ACL_USER:
- uid = make_kuid(from, le32_to_cpu(entry->e_id));
- entry->e_id = cpu_to_le32(from_kuid(to, uid));
+ kuid = make_kuid(from, le32_to_cpu(entry->e_id));
+ if (!uid_valid(kuid))
+ return -EOVERFLOW;
+ uid = from_kuid(to, kuid);
+ if (uid == (uid_t)-1)
+ return -EOVERFLOW;
+ entry->e_id = cpu_to_le32(uid);
break;
case ACL_GROUP:
- gid = make_kgid(from, le32_to_cpu(entry->e_id));
- entry->e_id = cpu_to_le32(from_kgid(to, gid));
+ kgid = make_kgid(from, le32_to_cpu(entry->e_id));
+ if (!gid_valid(kgid))
+ return -EOVERFLOW;
+ gid = from_kgid(to, kgid);
+ if (gid == (gid_t)-1)
+ return -EOVERFLOW;
+ entry->e_id = cpu_to_le32(gid);
break;
default:
break;
}
}
+
+ return 0;
}

-void posix_acl_fix_xattr_from_user(void *value, size_t size)
+int
+posix_acl_fix_xattr_from_user(struct user_namespace *target_ns, void *value,
+ size_t size)
{
- struct user_namespace *user_ns = current_user_ns();
- if (user_ns == &init_user_ns)
- return;
- posix_acl_fix_xattr_userns(&init_user_ns, user_ns, value, size);
+ struct user_namespace *source_ns = current_user_ns();
+ if (source_ns == target_ns)
+ return 0;
+ return posix_acl_fix_xattr_userns(target_ns, source_ns, value, size);
}

-void posix_acl_fix_xattr_to_user(void *value, size_t size)
+int
+posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
+ size_t size)
{
- struct user_namespace *user_ns = current_user_ns();
- if (user_ns == &init_user_ns)
- return;
- posix_acl_fix_xattr_userns(user_ns, &init_user_ns, value, size);
+ struct user_namespace *target_ns = current_user_ns();
+ if (target_ns == source_ns)
+ return 0;
+ return posix_acl_fix_xattr_userns(target_ns, source_ns, value, size);
}

/*
@@ -780,7 +798,7 @@ posix_acl_xattr_get(const struct xattr_handler *handler,
if (acl == NULL)
return -ENODATA;

- error = posix_acl_to_xattr(&init_user_ns, acl, value, size);
+ error = posix_acl_to_xattr(dentry->d_sb->s_user_ns, acl, value, size);
posix_acl_release(acl);

return error;
@@ -806,7 +824,8 @@ posix_acl_xattr_set(const struct xattr_handler *handler,
return -EPERM;

if (value) {
- acl = posix_acl_from_xattr(&init_user_ns, value, size);
+ acl = posix_acl_from_xattr(dentry->d_sb->s_user_ns, value,
+ size);
if (IS_ERR(acl))
return PTR_ERR(acl);

diff --git a/fs/xattr.c b/fs/xattr.c
index 4861322e28e8..c541121945cd 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -330,8 +330,12 @@ setxattr(struct dentry *d, const char __user *name, const void __user *value,
goto out;
}
if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
- (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
- posix_acl_fix_xattr_from_user(kvalue, size);
+ (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) {
+ error = posix_acl_fix_xattr_from_user(d->d_sb->s_user_ns,
+ kvalue, size);
+ if (error)
+ goto out;
+ }
}

error = vfs_setxattr(d, kname, kvalue, size, flags);
@@ -427,9 +431,14 @@ getxattr(struct dentry *d, const char __user *name, void __user *value,
error = vfs_getxattr(d, kname, kvalue, size);
if (error > 0) {
if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
- (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
- posix_acl_fix_xattr_to_user(kvalue, size);
- if (size && copy_to_user(value, kvalue, error))
+ (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) {
+ int ret;
+ ret = posix_acl_fix_xattr_to_user(d->d_sb->s_user_ns,
+ kvalue, size);
+ if (ret)
+ error = ret;
+ }
+ if (error > 0 && size && copy_to_user(value, kvalue, error))
error = -EFAULT;
} else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
/* The file system tried to returned a value bigger
diff --git a/include/linux/posix_acl_xattr.h b/include/linux/posix_acl_xattr.h
index e5e8ec40278d..5dec6b10951a 100644
--- a/include/linux/posix_acl_xattr.h
+++ b/include/linux/posix_acl_xattr.h
@@ -49,14 +49,23 @@ posix_acl_xattr_count(size_t size)
}

#ifdef CONFIG_FS_POSIX_ACL
-void posix_acl_fix_xattr_from_user(void *value, size_t size);
-void posix_acl_fix_xattr_to_user(void *value, size_t size);
+int posix_acl_fix_xattr_from_user(struct user_namespace *target_ns,
+ void *value, size_t size);
+int posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
+ size_t size);
#else
-static inline void posix_acl_fix_xattr_from_user(void *value, size_t size)
+static inline int
+posix_acl_fix_xattr_from_user(struct user_namespace *target_ns, void *value,
+ size_t size)
{
+ return 0;
}
-static inline void posix_acl_fix_xattr_to_user(void *value, size_t size)
+
+static inline int
+posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
+ size_t size)
{
+ return 0;
}
#endif

--
1.9.1