Am Di., 17. Juni 2025 um 17:45 Uhr schrieb Christian Brauner
<brauner@xxxxxxxxxx>:
>
> Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> ---
> fs/pidfs.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 92 insertions(+), 2 deletions(-)
>
> diff --git a/fs/pidfs.c b/fs/pidfs.c
> index 1343bfc60e3f..b1968f628417 100644
> --- a/fs/pidfs.c
> +++ b/fs/pidfs.c
> @@ -21,6 +21,7 @@
> #include <linux/utsname.h>
> #include <net/net_namespace.h>
> #include <linux/coredump.h>
> +#include <linux/xattr.h>
>
> #include "internal.h"
> #include "mount.h"
> @@ -40,6 +41,7 @@
> #define PIDFS_PID_DEAD ERR_PTR(-ESRCH)
>
> static struct kmem_cache *pidfs_cachep __ro_after_init;
> +static struct kmem_cache *pidfs_attrs_cachep __ro_after_init;
>
> /*
> * Stashes information that userspace needs to access even after the
> @@ -51,9 +53,14 @@ struct pidfs_exit_info {
> __u32 coredump_mask;
> };
>
> +struct pidfs_attrs {
> + struct simple_xattrs xattrs;
> +};
> +
> struct pidfs_inode {
> struct pidfs_exit_info __pei;
> struct pidfs_exit_info *exit_info;
> + struct pidfs_attrs *attrs;
> struct inode vfs_inode;
> };
>
> @@ -672,15 +679,34 @@ static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path,
> return anon_inode_getattr(idmap, path, stat, request_mask, query_flags);
> }
>
> +static ssize_t pidfs_listxattr(struct dentry *dentry, char *buf, size_t size)
> +{
> + struct inode *inode = d_inode(dentry);
> + struct pidfs_attrs *attrs;
> +
> + attrs = READ_ONCE(pidfs_i(inode)->attrs);
> + if (!attrs)
> + return -ENODATA;
> +
> + return simple_xattr_list(inode, &attrs->xattrs, buf, size);
> +}
> +
> static const struct inode_operations pidfs_inode_operations = {
> - .getattr = pidfs_getattr,
> - .setattr = pidfs_setattr,
> + .getattr = pidfs_getattr,
> + .setattr = pidfs_setattr,
> + .listxattr = pidfs_listxattr,
> };
>
> static void pidfs_evict_inode(struct inode *inode)
> {
> struct pid *pid = inode->i_private;
> + struct pidfs_attrs *attrs;
>
> + attrs = READ_ONCE(pidfs_i(inode)->attrs);
> + if (attrs) {
> + simple_xattrs_free(&attrs->xattrs, NULL);
> + kmem_cache_free(pidfs_attrs_cachep, attrs);
> + }
> clear_inode(inode);
> put_pid(pid);
> }
> @@ -695,6 +721,7 @@ static struct inode *pidfs_alloc_inode(struct super_block *sb)
>
> memset(&pi->__pei, 0, sizeof(pi->__pei));
> pi->exit_info = NULL;
> + pi->attrs = NULL;
>
> return &pi->vfs_inode;
> }
> @@ -951,6 +978,63 @@ static const struct stashed_operations pidfs_stashed_ops = {
> .put_data = pidfs_put_data,
> };
>
> +static int pidfs_xattr_get(const struct xattr_handler *handler,
> + struct dentry *unused, struct inode *inode,
> + const char *suffix, void *value, size_t size)
> +{
> + const char *name;
> + struct pidfs_attrs *attrs;
> +
> + attrs = READ_ONCE(pidfs_i(inode)->attrs);
> + if (!attrs)
> + return -ENODATA;
> +
> + name = xattr_full_name(handler, suffix);
> + return simple_xattr_get(&attrs->xattrs, name, value, size);
> +}
> +
> +static int pidfs_xattr_set(const struct xattr_handler *handler,
> + struct mnt_idmap *idmap, struct dentry *unused,
> + struct inode *inode, const char *suffix,
> + const void *value, size_t size, int flags)
> +{
> + const char *name;
> + struct pidfs_attrs *attrs;
> + struct simple_xattr *old_xattr;
> +
> + /* Make sure we're the only one here. */
> + WARN_ON_ONCE(!inode_is_locked(inode));
> +
> + attrs = READ_ONCE(pidfs_i(inode)->attrs);
> + if (!attrs) {
> + attrs = kmem_cache_zalloc(pidfs_attrs_cachep, GFP_KERNEL);
> + if (!attrs)
> + return -ENOMEM;
> +
> + simple_xattrs_init(&attrs->xattrs);
> + smp_store_release(&pidfs_i(inode)->attrs, attrs);
> + }
> +
> + name = xattr_full_name(handler, suffix);
> + old_xattr = simple_xattr_set(&attrs->xattrs, name, value, size, flags);
> + if (IS_ERR(old_xattr))
> + return PTR_ERR(old_xattr);
> +
> + simple_xattr_free(old_xattr);
> + return 0;
> +}
> +
> +static const struct xattr_handler pidfs_trusted_xattr_handler = {
> + .prefix = XATTR_TRUSTED_PREFIX,
> + .get = pidfs_xattr_get,
> + .set = pidfs_xattr_set,
> +};
> +
> +static const struct xattr_handler *const pidfs_xattr_handlers[] = {
> + &pidfs_trusted_xattr_handler,
> + NULL
> +};
> +
> static int pidfs_init_fs_context(struct fs_context *fc)
> {
> struct pseudo_fs_context *ctx;
> @@ -964,6 +1048,7 @@ static int pidfs_init_fs_context(struct fs_context *fc)
> ctx->ops = &pidfs_sops;
> ctx->eops = &pidfs_export_operations;
> ctx->dops = &pidfs_dentry_operations;
> + ctx->xattr = pidfs_xattr_handlers;
> fc->s_fs_info = (void *)&pidfs_stashed_ops;
> return 0;
> }
> @@ -1073,6 +1158,11 @@ void __init pidfs_init(void)
> (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT |
> SLAB_ACCOUNT | SLAB_PANIC),
> pidfs_inode_init_once);
> +
> + pidfs_attrs_cachep = kmem_cache_create("pidfs_attrs_cache",
> + sizeof(struct pidfs_attrs), 0,
> + SLAB_PANIC, NULL);
nit: WDYT about adding SLAB_ACCOUNT too?
> +
> pidfs_mnt = kern_mount(&pidfs_type);
> if (IS_ERR(pidfs_mnt))
> panic("Failed to mount pidfs pseudo filesystem");
>
> --
> 2.47.2
>
