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authorDaniel Xu <dxu@dxuuu.xyz>2020-03-12 23:03:16 +0300
committerTejun Heo <tj@kernel.org>2020-03-16 22:53:47 +0300
commit0c47383ba3bd10877956e41149d19644fba937d1 (patch)
treec3d3b420f3a961c2fb4ab56feed39bf129933939 /fs/kernfs/inode.c
parenta46a22955bae16fc5a756af7188d3ccb25c3f797 (diff)
downloadlinux-0c47383ba3bd10877956e41149d19644fba937d1.tar.xz
kernfs: Add option to enable user xattrs
User extended attributes are useful as metadata storage for kernfs consumers like cgroups. Especially in the case of cgroups, it is useful to have a central metadata store that multiple processes/services can use to coordinate actions. A concrete example is for userspace out of memory killers. We want to let delegated cgroup subtree owners (running as non-root) to be able to say "please avoid killing this cgroup". This is especially important for desktop linux as delegated subtrees owners are less likely to run as root. This patch introduces a new flag, KERNFS_ROOT_SUPPORT_USER_XATTR, that lets kernfs consumers enable user xattr support. An initial limit of 128 entries or 128KB -- whichever is hit first -- is placed per cgroup because xattrs come from kernel memory and we don't want to let unprivileged users accidentally eat up too much kernel memory. Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> Acked-by: Chris Down <chris@chrisdown.name> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'fs/kernfs/inode.c')
-rw-r--r--fs/kernfs/inode.c89
1 files changed, 89 insertions, 0 deletions
diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index 5f10ae95fbfa..fc2469a20fed 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -53,6 +53,8 @@ static struct kernfs_iattrs *__kernfs_iattrs(struct kernfs_node *kn, int alloc)
kn->iattr->ia_ctime = kn->iattr->ia_atime;
simple_xattrs_init(&kn->iattr->xattrs);
+ atomic_set(&kn->iattr->nr_user_xattrs, 0);
+ atomic_set(&kn->iattr->user_xattr_size, 0);
out_unlock:
ret = kn->iattr;
mutex_unlock(&iattr_mutex);
@@ -327,6 +329,86 @@ static int kernfs_vfs_xattr_set(const struct xattr_handler *handler,
return kernfs_xattr_set(kn, name, value, size, flags);
}
+static int kernfs_vfs_user_xattr_add(struct kernfs_node *kn,
+ const char *full_name,
+ struct simple_xattrs *xattrs,
+ const void *value, size_t size, int flags)
+{
+ atomic_t *sz = &kn->iattr->user_xattr_size;
+ atomic_t *nr = &kn->iattr->nr_user_xattrs;
+ ssize_t removed_size;
+ int ret;
+
+ if (atomic_inc_return(nr) > KERNFS_MAX_USER_XATTRS) {
+ ret = -ENOSPC;
+ goto dec_count_out;
+ }
+
+ if (atomic_add_return(size, sz) > KERNFS_USER_XATTR_SIZE_LIMIT) {
+ ret = -ENOSPC;
+ goto dec_size_out;
+ }
+
+ ret = simple_xattr_set(xattrs, full_name, value, size, flags,
+ &removed_size);
+
+ if (!ret && removed_size >= 0)
+ size = removed_size;
+ else if (!ret)
+ return 0;
+dec_size_out:
+ atomic_sub(size, sz);
+dec_count_out:
+ atomic_dec(nr);
+ return ret;
+}
+
+static int kernfs_vfs_user_xattr_rm(struct kernfs_node *kn,
+ const char *full_name,
+ struct simple_xattrs *xattrs,
+ const void *value, size_t size, int flags)
+{
+ atomic_t *sz = &kn->iattr->user_xattr_size;
+ atomic_t *nr = &kn->iattr->nr_user_xattrs;
+ ssize_t removed_size;
+ int ret;
+
+ ret = simple_xattr_set(xattrs, full_name, value, size, flags,
+ &removed_size);
+
+ if (removed_size >= 0) {
+ atomic_sub(removed_size, sz);
+ atomic_dec(nr);
+ }
+
+ return ret;
+}
+
+static int kernfs_vfs_user_xattr_set(const struct xattr_handler *handler,
+ struct dentry *unused, struct inode *inode,
+ const char *suffix, const void *value,
+ size_t size, int flags)
+{
+ const char *full_name = xattr_full_name(handler, suffix);
+ struct kernfs_node *kn = inode->i_private;
+ struct kernfs_iattrs *attrs;
+
+ if (!(kernfs_root(kn)->flags & KERNFS_ROOT_SUPPORT_USER_XATTR))
+ return -EOPNOTSUPP;
+
+ attrs = kernfs_iattrs(kn);
+ if (!attrs)
+ return -ENOMEM;
+
+ if (value)
+ return kernfs_vfs_user_xattr_add(kn, full_name, &attrs->xattrs,
+ value, size, flags);
+ else
+ return kernfs_vfs_user_xattr_rm(kn, full_name, &attrs->xattrs,
+ value, size, flags);
+
+}
+
static const struct xattr_handler kernfs_trusted_xattr_handler = {
.prefix = XATTR_TRUSTED_PREFIX,
.get = kernfs_vfs_xattr_get,
@@ -339,8 +421,15 @@ static const struct xattr_handler kernfs_security_xattr_handler = {
.set = kernfs_vfs_xattr_set,
};
+static const struct xattr_handler kernfs_user_xattr_handler = {
+ .prefix = XATTR_USER_PREFIX,
+ .get = kernfs_vfs_xattr_get,
+ .set = kernfs_vfs_user_xattr_set,
+};
+
const struct xattr_handler *kernfs_xattr_handlers[] = {
&kernfs_trusted_xattr_handler,
&kernfs_security_xattr_handler,
+ &kernfs_user_xattr_handler,
NULL
};