Mike Christie
2021-Jun-29 16:53 UTC
[PATCH 2/3] kernel/fork, cred.c: allow copy_process to take user
On 6/29/21 8:04 AM, Christian Brauner wrote:> On Wed, Jun 23, 2021 at 10:08:03PM -0500, Mike Christie wrote: >> This allows kthread to pass copy_process the user we want to check for the >> RLIMIT_NPROC limit for and also charge for the new process. It will be used >> by vhost where userspace has that driver create threads but the kthreadd >> thread is checked/charged. >> >> Signed-off-by: Mike Christie <michael.christie at oracle.com> >> --- >> include/linux/cred.h | 3 ++- >> kernel/cred.c | 7 ++++--- >> kernel/fork.c | 12 +++++++----- >> 3 files changed, 13 insertions(+), 9 deletions(-) >> >> diff --git a/include/linux/cred.h b/include/linux/cred.h >> index 14971322e1a0..9a2c1398cdd4 100644 >> --- a/include/linux/cred.h >> +++ b/include/linux/cred.h >> @@ -153,7 +153,8 @@ struct cred { >> >> extern void __put_cred(struct cred *); >> extern void exit_creds(struct task_struct *); >> -extern int copy_creds(struct task_struct *, unsigned long); >> +extern int copy_creds(struct task_struct *, unsigned long, >> + struct user_struct *); >> extern const struct cred *get_task_cred(struct task_struct *); >> extern struct cred *cred_alloc_blank(void); >> extern struct cred *prepare_creds(void); >> diff --git a/kernel/cred.c b/kernel/cred.c >> index e1d274cd741b..e006aafa8f05 100644 >> --- a/kernel/cred.c >> +++ b/kernel/cred.c >> @@ -330,7 +330,8 @@ struct cred *prepare_exec_creds(void) >> * The new process gets the current process's subjective credentials as its >> * objective and subjective credentials >> */ >> -int copy_creds(struct task_struct *p, unsigned long clone_flags) >> +int copy_creds(struct task_struct *p, unsigned long clone_flags, >> + struct user_struct *user) >> { >> struct cred *new; >> int ret; >> @@ -351,7 +352,7 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) >> kdebug("share_creds(%p{%d,%d})", >> p->cred, atomic_read(&p->cred->usage), >> read_cred_subscribers(p->cred)); >> - atomic_inc(&p->cred->user->processes); >> + atomic_inc(&user->processes); > > Hey Mike, > > This won't work anymore since this has moved into ucounts. So in v5.14 > atomic_inc(&p->cred->user->processes); > will have been replaced by > inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); >Will do.> From what I can see from your code vhost will always create this kthread > for current. So you could e.g. add an internal flag/bitfield entry to > struct kernel_clone_args that you can use to tell copy_creds() that you > want to charge this thread against current's process limit.If I understood you, I don't think a flag/bit will work. When vhost does a kthread call we do kthread_create -> __kthread_create_on_node. This creates a tmp kthread_create_info struct and adds it to the kthread_create_list list. It then wakes up the kthreadd thread. kthreadd will then loop over the list, and do the: kernel_thread -> kernel_clone -> copy_process -> copy_creds So copy_creds sees current == kthreadd. I think I would have to add a task_struct pointer to kernel_clone_args and kthread_create_info. If copy_creds sees kernel_clone_args->user_task then it would use that.
michael.christie at oracle.com
2021-Jul-01 23:59 UTC
[PATCH 2/3] kernel/fork, cred.c: allow copy_process to take user
On 6/29/21 11:53 AM, Mike Christie wrote:> On 6/29/21 8:04 AM, Christian Brauner wrote: >> On Wed, Jun 23, 2021 at 10:08:03PM -0500, Mike Christie wrote: >>> This allows kthread to pass copy_process the user we want to check for the >>> RLIMIT_NPROC limit for and also charge for the new process. It will be used >>> by vhost where userspace has that driver create threads but the kthreadd >>> thread is checked/charged. >>> >>> Signed-off-by: Mike Christie <michael.christie at oracle.com> >>> --- >>> include/linux/cred.h | 3 ++- >>> kernel/cred.c | 7 ++++--- >>> kernel/fork.c | 12 +++++++----- >>> 3 files changed, 13 insertions(+), 9 deletions(-) >>> >>> diff --git a/include/linux/cred.h b/include/linux/cred.h >>> index 14971322e1a0..9a2c1398cdd4 100644 >>> --- a/include/linux/cred.h >>> +++ b/include/linux/cred.h >>> @@ -153,7 +153,8 @@ struct cred { >>> >>> extern void __put_cred(struct cred *); >>> extern void exit_creds(struct task_struct *); >>> -extern int copy_creds(struct task_struct *, unsigned long); >>> +extern int copy_creds(struct task_struct *, unsigned long, >>> + struct user_struct *); >>> extern const struct cred *get_task_cred(struct task_struct *); >>> extern struct cred *cred_alloc_blank(void); >>> extern struct cred *prepare_creds(void); >>> diff --git a/kernel/cred.c b/kernel/cred.c >>> index e1d274cd741b..e006aafa8f05 100644 >>> --- a/kernel/cred.c >>> +++ b/kernel/cred.c >>> @@ -330,7 +330,8 @@ struct cred *prepare_exec_creds(void) >>> * The new process gets the current process's subjective credentials as its >>> * objective and subjective credentials >>> */ >>> -int copy_creds(struct task_struct *p, unsigned long clone_flags) >>> +int copy_creds(struct task_struct *p, unsigned long clone_flags, >>> + struct user_struct *user) >>> { >>> struct cred *new; >>> int ret; >>> @@ -351,7 +352,7 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) >>> kdebug("share_creds(%p{%d,%d})", >>> p->cred, atomic_read(&p->cred->usage), >>> read_cred_subscribers(p->cred)); >>> - atomic_inc(&p->cred->user->processes); >>> + atomic_inc(&user->processes); >> >> Hey Mike, >> >> This won't work anymore since this has moved into ucounts. So in v5.14 >> atomic_inc(&p->cred->user->processes); >> will have been replaced by >> inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); >> > Will do. > >> From what I can see from your code vhost will always create this kthread >> for current. So you could e.g. add an internal flag/bitfield entry to >> struct kernel_clone_args that you can use to tell copy_creds() that you >> want to charge this thread against current's process limit. > > If I understood you, I don't think a flag/bit will work. When vhost does > a kthread call we do kthread_create -> __kthread_create_on_node. This creates > a tmp kthread_create_info struct and adds it to the kthread_create_list list. > It then wakes up the kthreadd thread. kthreadd will then loop over the list, > and do the: > > kernel_thread -> kernel_clone -> copy_process -> copy_creds > > So copy_creds sees current == kthreadd. > > I think I would have to add a task_struct pointer to kernel_clone_args > and kthread_create_info. If copy_creds sees kernel_clone_args->user_task > then it would use that.One question/clarification. For 5.14, I could pass in the struct task_struct or struct ucounts (in a previous mail I wrote user_struct). I could also just have vhost.c do inc_rlimit_ucounts and is_ucounts_overlimit directly.