* [PATCH -next] fork.c: Move check of clone NEWIPC and SYSVSEM to copy_process
@ 2017-11-26 16:06 Marcos Paulo de Souza
2017-11-30 10:04 ` Michal Hocko
0 siblings, 1 reply; 4+ messages in thread
From: Marcos Paulo de Souza @ 2017-11-26 16:06 UTC (permalink / raw)
Cc: Marcos Paulo de Souza, Andrew Morton, Ingo Molnar, Rik van Riel,
Michal Hocko, Stephen Rothwell, Kirill A. Shutemov, Jiri Olsa,
Hari Bathini, Peter Zijlstra, Arnaldo Carvalho de Melo,
linux-kernel
Currently this check for CLONE_NEWIPC with CLONE_SYSVSEM is done inside
copy_namespaces, resulting in a handful of error paths being executed if
these flags were used together. So, move this check to the beginning of
copy_process, exiting earlier if the condition is true.
This move is safe because copy_namespaces is called just from
copy_process function.
Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
---
kernel/fork.c | 11 +++++++++++
kernel/nsproxy.c | 11 -----------
2 files changed, 11 insertions(+), 11 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index 2113e252cb9d..691f9ba135fc 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1600,6 +1600,17 @@ static __latent_entropy struct task_struct *copy_process(
return ERR_PTR(-EINVAL);
/*
+ * CLONE_NEWIPC must detach from the undolist: after switching
+ * to a new ipc namespace, the semaphore arrays from the old
+ * namespace are unreachable. In clone parlance, CLONE_SYSVSEM
+ * means share undolist with parent, so we must forbid using
+ * it along with CLONE_NEWIPC.
+ */
+ if ((clone_flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
+ (CLONE_NEWIPC | CLONE_SYSVSEM))
+ return ERR_PTR(-EINVAL);
+
+ /*
* Thread groups must share signals as well, and detached threads
* can only be started up within the thread group.
*/
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index f6c5d330059a..30882727dff5 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -151,17 +151,6 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
if (!ns_capable(user_ns, CAP_SYS_ADMIN))
return -EPERM;
- /*
- * CLONE_NEWIPC must detach from the undolist: after switching
- * to a new ipc namespace, the semaphore arrays from the old
- * namespace are unreachable. In clone parlance, CLONE_SYSVSEM
- * means share undolist with parent, so we must forbid using
- * it along with CLONE_NEWIPC.
- */
- if ((flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
- (CLONE_NEWIPC | CLONE_SYSVSEM))
- return -EINVAL;
-
new_ns = create_new_namespaces(flags, tsk, user_ns, tsk->fs);
if (IS_ERR(new_ns))
return PTR_ERR(new_ns);
--
2.13.6
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH -next] fork.c: Move check of clone NEWIPC and SYSVSEM to copy_process
2017-11-30 10:04 ` Michal Hocko
@ 2017-11-30 0:33 ` Marcos Paulo de Souza
2017-12-01 8:19 ` Michal Hocko
0 siblings, 1 reply; 4+ messages in thread
From: Marcos Paulo de Souza @ 2017-11-30 0:33 UTC (permalink / raw)
To: Michal Hocko
Cc: Andrew Morton, Ingo Molnar, Rik van Riel, Stephen Rothwell,
Kirill A. Shutemov, Jiri Olsa, Hari Bathini, Peter Zijlstra,
Arnaldo Carvalho de Melo, Eric W. Biederman, linux-kernel
On Thu, Nov 30, 2017 at 11:04:06AM +0100, Michal Hocko wrote:
> CC Eric
>
> On Sun 26-11-17 14:06:52, Marcos Paulo de Souza wrote:
> > Currently this check for CLONE_NEWIPC with CLONE_SYSVSEM is done inside
> > copy_namespaces, resulting in a handful of error paths being executed if
> > these flags were used together. So, move this check to the beginning of
> > copy_process, exiting earlier if the condition is true.
> >
> > This move is safe because copy_namespaces is called just from
> > copy_process function.
This change is introduced right below the point where clone_flags is already
checking for inconsistencies in namespace flags[1], and returns EINVAL when
conflicting flags are informed together.
In this case, it's easier to return early when conflicting flags are informed at
the beginning, so moving a namespace check to where namespaces are already being
sanitized makes sense. If the code stays where it is now, and a user calls clone
syscalls informing CLONE_NEWIPC | CLONE_SYSVSEM, the code will need to undo a
lot of work before returning the same EINVAL[2].
[1] https://elixir.free-electrons.com/linux/latest/source/kernel/fork.c#L1552
[2] https://elixir.free-electrons.com/linux/latest/source/kernel/fork.c#L1953
>
> I am not familiar with the code all that much but the justification is
> not clear to me. Thesea re namespace related flags so why should we pull
> them out of copy_namespaces. I do not see any simplifications in the
> error code paths or something like that.
>
> > Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
> > ---
> > kernel/fork.c | 11 +++++++++++
> > kernel/nsproxy.c | 11 -----------
> > 2 files changed, 11 insertions(+), 11 deletions(-)
> >
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 2113e252cb9d..691f9ba135fc 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -1600,6 +1600,17 @@ static __latent_entropy struct task_struct *copy_process(
> > return ERR_PTR(-EINVAL);
> >
> > /*
> > + * CLONE_NEWIPC must detach from the undolist: after switching
> > + * to a new ipc namespace, the semaphore arrays from the old
> > + * namespace are unreachable. In clone parlance, CLONE_SYSVSEM
> > + * means share undolist with parent, so we must forbid using
> > + * it along with CLONE_NEWIPC.
> > + */
> > + if ((clone_flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
> > + (CLONE_NEWIPC | CLONE_SYSVSEM))
> > + return ERR_PTR(-EINVAL);
> > +
> > + /*
> > * Thread groups must share signals as well, and detached threads
> > * can only be started up within the thread group.
> > */
> > diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> > index f6c5d330059a..30882727dff5 100644
> > --- a/kernel/nsproxy.c
> > +++ b/kernel/nsproxy.c
> > @@ -151,17 +151,6 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
> > if (!ns_capable(user_ns, CAP_SYS_ADMIN))
> > return -EPERM;
> >
> > - /*
> > - * CLONE_NEWIPC must detach from the undolist: after switching
> > - * to a new ipc namespace, the semaphore arrays from the old
> > - * namespace are unreachable. In clone parlance, CLONE_SYSVSEM
> > - * means share undolist with parent, so we must forbid using
> > - * it along with CLONE_NEWIPC.
> > - */
> > - if ((flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
> > - (CLONE_NEWIPC | CLONE_SYSVSEM))
> > - return -EINVAL;
> > -
> > new_ns = create_new_namespaces(flags, tsk, user_ns, tsk->fs);
> > if (IS_ERR(new_ns))
> > return PTR_ERR(new_ns);
> > --
> > 2.13.6
> >
>
> --
> Michal Hocko
> SUSE Labs
--
Thanks,
Marcos
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH -next] fork.c: Move check of clone NEWIPC and SYSVSEM to copy_process
2017-11-26 16:06 [PATCH -next] fork.c: Move check of clone NEWIPC and SYSVSEM to copy_process Marcos Paulo de Souza
@ 2017-11-30 10:04 ` Michal Hocko
2017-11-30 0:33 ` Marcos Paulo de Souza
0 siblings, 1 reply; 4+ messages in thread
From: Michal Hocko @ 2017-11-30 10:04 UTC (permalink / raw)
To: Marcos Paulo de Souza
Cc: Andrew Morton, Ingo Molnar, Rik van Riel, Stephen Rothwell,
Kirill A. Shutemov, Jiri Olsa, Hari Bathini, Peter Zijlstra,
Arnaldo Carvalho de Melo, Eric W. Biederman, linux-kernel
CC Eric
On Sun 26-11-17 14:06:52, Marcos Paulo de Souza wrote:
> Currently this check for CLONE_NEWIPC with CLONE_SYSVSEM is done inside
> copy_namespaces, resulting in a handful of error paths being executed if
> these flags were used together. So, move this check to the beginning of
> copy_process, exiting earlier if the condition is true.
>
> This move is safe because copy_namespaces is called just from
> copy_process function.
I am not familiar with the code all that much but the justification is
not clear to me. Thesea re namespace related flags so why should we pull
them out of copy_namespaces. I do not see any simplifications in the
error code paths or something like that.
> Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
> ---
> kernel/fork.c | 11 +++++++++++
> kernel/nsproxy.c | 11 -----------
> 2 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 2113e252cb9d..691f9ba135fc 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1600,6 +1600,17 @@ static __latent_entropy struct task_struct *copy_process(
> return ERR_PTR(-EINVAL);
>
> /*
> + * CLONE_NEWIPC must detach from the undolist: after switching
> + * to a new ipc namespace, the semaphore arrays from the old
> + * namespace are unreachable. In clone parlance, CLONE_SYSVSEM
> + * means share undolist with parent, so we must forbid using
> + * it along with CLONE_NEWIPC.
> + */
> + if ((clone_flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
> + (CLONE_NEWIPC | CLONE_SYSVSEM))
> + return ERR_PTR(-EINVAL);
> +
> + /*
> * Thread groups must share signals as well, and detached threads
> * can only be started up within the thread group.
> */
> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index f6c5d330059a..30882727dff5 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -151,17 +151,6 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
> if (!ns_capable(user_ns, CAP_SYS_ADMIN))
> return -EPERM;
>
> - /*
> - * CLONE_NEWIPC must detach from the undolist: after switching
> - * to a new ipc namespace, the semaphore arrays from the old
> - * namespace are unreachable. In clone parlance, CLONE_SYSVSEM
> - * means share undolist with parent, so we must forbid using
> - * it along with CLONE_NEWIPC.
> - */
> - if ((flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
> - (CLONE_NEWIPC | CLONE_SYSVSEM))
> - return -EINVAL;
> -
> new_ns = create_new_namespaces(flags, tsk, user_ns, tsk->fs);
> if (IS_ERR(new_ns))
> return PTR_ERR(new_ns);
> --
> 2.13.6
>
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH -next] fork.c: Move check of clone NEWIPC and SYSVSEM to copy_process
2017-11-30 0:33 ` Marcos Paulo de Souza
@ 2017-12-01 8:19 ` Michal Hocko
0 siblings, 0 replies; 4+ messages in thread
From: Michal Hocko @ 2017-12-01 8:19 UTC (permalink / raw)
To: Marcos Paulo de Souza
Cc: Andrew Morton, Ingo Molnar, Rik van Riel, Stephen Rothwell,
Kirill A. Shutemov, Jiri Olsa, Hari Bathini, Peter Zijlstra,
Arnaldo Carvalho de Melo, Eric W. Biederman, linux-kernel
On Wed 29-11-17 22:33:43, Marcos Paulo de Souza wrote:
> On Thu, Nov 30, 2017 at 11:04:06AM +0100, Michal Hocko wrote:
> > CC Eric
> >
> > On Sun 26-11-17 14:06:52, Marcos Paulo de Souza wrote:
> > > Currently this check for CLONE_NEWIPC with CLONE_SYSVSEM is done inside
> > > copy_namespaces, resulting in a handful of error paths being executed if
> > > these flags were used together. So, move this check to the beginning of
> > > copy_process, exiting earlier if the condition is true.
> > >
> > > This move is safe because copy_namespaces is called just from
> > > copy_process function.
>
> This change is introduced right below the point where clone_flags is already
> checking for inconsistencies in namespace flags[1], and returns EINVAL when
> conflicting flags are informed together.
>
> In this case, it's easier to return early when conflicting flags are informed at
> the beginning, so moving a namespace check to where namespaces are already being
> sanitized makes sense.
What doe easier mean in this context?
> If the code stays where it is now, and a user calls clone
> syscalls informing CLONE_NEWIPC | CLONE_SYSVSEM, the code will need to undo a
> lot of work before returning the same EINVAL[2].
And why do we care about that error path? Does it trigger that often?
Do not take me wrong. I am not saying the patch is incorrect or wrong.
The changelog lacks the justification and explanation _why_ do we care
at all. A rarely failing path reorganization doesn't sound too
interesting to me. I cannot judge the cleanup aspect of this though but
from a very naive diffstat POV it doesn't look like a huge win to me.
> [1] https://elixir.free-electrons.com/linux/latest/source/kernel/fork.c#L1552
> [2] https://elixir.free-electrons.com/linux/latest/source/kernel/fork.c#L1953
>
> >
> > I am not familiar with the code all that much but the justification is
> > not clear to me. Thesea re namespace related flags so why should we pull
> > them out of copy_namespaces. I do not see any simplifications in the
> > error code paths or something like that.
> >
> > > Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
> > > ---
> > > kernel/fork.c | 11 +++++++++++
> > > kernel/nsproxy.c | 11 -----------
> > > 2 files changed, 11 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/kernel/fork.c b/kernel/fork.c
> > > index 2113e252cb9d..691f9ba135fc 100644
> > > --- a/kernel/fork.c
> > > +++ b/kernel/fork.c
> > > @@ -1600,6 +1600,17 @@ static __latent_entropy struct task_struct *copy_process(
> > > return ERR_PTR(-EINVAL);
> > >
> > > /*
> > > + * CLONE_NEWIPC must detach from the undolist: after switching
> > > + * to a new ipc namespace, the semaphore arrays from the old
> > > + * namespace are unreachable. In clone parlance, CLONE_SYSVSEM
> > > + * means share undolist with parent, so we must forbid using
> > > + * it along with CLONE_NEWIPC.
> > > + */
> > > + if ((clone_flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
> > > + (CLONE_NEWIPC | CLONE_SYSVSEM))
> > > + return ERR_PTR(-EINVAL);
> > > +
> > > + /*
> > > * Thread groups must share signals as well, and detached threads
> > > * can only be started up within the thread group.
> > > */
> > > diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> > > index f6c5d330059a..30882727dff5 100644
> > > --- a/kernel/nsproxy.c
> > > +++ b/kernel/nsproxy.c
> > > @@ -151,17 +151,6 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
> > > if (!ns_capable(user_ns, CAP_SYS_ADMIN))
> > > return -EPERM;
> > >
> > > - /*
> > > - * CLONE_NEWIPC must detach from the undolist: after switching
> > > - * to a new ipc namespace, the semaphore arrays from the old
> > > - * namespace are unreachable. In clone parlance, CLONE_SYSVSEM
> > > - * means share undolist with parent, so we must forbid using
> > > - * it along with CLONE_NEWIPC.
> > > - */
> > > - if ((flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
> > > - (CLONE_NEWIPC | CLONE_SYSVSEM))
> > > - return -EINVAL;
> > > -
> > > new_ns = create_new_namespaces(flags, tsk, user_ns, tsk->fs);
> > > if (IS_ERR(new_ns))
> > > return PTR_ERR(new_ns);
> > > --
> > > 2.13.6
> > >
> >
> > --
> > Michal Hocko
> > SUSE Labs
>
> --
> Thanks,
> Marcos
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 4+ messages in thread
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2017-11-26 16:06 [PATCH -next] fork.c: Move check of clone NEWIPC and SYSVSEM to copy_process Marcos Paulo de Souza
2017-11-30 10:04 ` Michal Hocko
2017-11-30 0:33 ` Marcos Paulo de Souza
2017-12-01 8:19 ` Michal Hocko
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