On Wed 04-11-26 18:47:00, Christian Brauner wrote:
> proc_sys_fill_cache() creates the inode of an entry that has no dentry
> yet. Since ace0c791e6c3 ("proc/sysctl: Don't grab i_lock under
> sysctl_lock.") proc_sys_make_inode() refuses to do that once the table
> is being unregistered and fails with -ENOENT. readdir takes every table
> it lists into use and unregister_sysctl_table() marks the table as
> being unregistered before it waits for readdir to let go of it. So an
> entry that is unregistered right then makes proc_sys_fill_cache() fail,
> proc_sys_readdir() stops there and returns 0. If that getdents64() call
> hadn't emitted anything before that entry userspace sees the end of the
> directory and never gets the entries behind it. A listing of
> /proc/sys/net/ipv6/conf can end early that way while a device goes
> away.
>
> So skip an entry whose table is being unregistered, like readdir
> already skips a link it can't follow. Lookup treats such an entry as
> gone too since ea5751ccd665 ("proc/sysctl: don't return ENOMEM on
> lookup when a table is unregistering").
>
> Fixes: ace0c791e6c3 ("proc/sysctl: Don't grab i_lock under sysctl_lock.")
> Cc: [email protected]
> Signed-off-by: Christian Brauner (Amutable) <[email protected]>
Looks sane. Feel free to add:
Reviewed-by: Jan Kara <[email protected]>
Honza
> ---
> fs/proc/proc_sysctl.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 6c0859c66563..b4a309d49698 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -704,6 +704,9 @@ static bool proc_sys_fill_cache(struct file *file,
> if (unlikely(res)) {
> dput(child);
>
> + /* skip an entry whose table is being
> unregistered */
> + if (res == ERR_PTR(-ENOENT))
> + return true;
> if (IS_ERR(res))
> return false;
>
>
> --
> 2.53.0
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
