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author | 2020-03-12 13:03:16 -0700 | |
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committer | 2020-03-16 15:53:47 -0400 | |
commit | 0c47383ba3bd10877956e41149d19644fba937d1 (patch) | |
tree | c3d3b420f3a961c2fb4ab56feed39bf129933939 /fs/kernfs/inode.c | |
parent | kernfs: Add removed_size out param for simple_xattr_set (diff) | |
download | linux-0c47383ba3bd10877956e41149d19644fba937d1.tar.gz linux-0c47383ba3bd10877956e41149d19644fba937d1.tar.bz2 linux-0c47383ba3bd10877956e41149d19644fba937d1.zip |
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.c | 89 |
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 }; |