Re: [PATCH 2/2] fix sys_unshare()+SEM_UNDO: perform an implicitCLONE_SYSVSEM in CLONE_NEWIPC

[Serge E. Hallyn]

Quoting Manfred Spraul (manfred@xxxxxxxxxxxxxxxx):
> sys_unshare(CLONE_NEWIPC) doesn't handle the undo lists properly, this can
> cause a kernel memory corruption. CLONE_NEWIPC must detach from the existing
> undo lists.
> Fix, part 2: perform an implicit CLONE_SYSVSEM in CLONE_NEWIPC.
> CLONE_NEWIPC creates a new IPC namespace, the task cannot access the
> existing semaphore arrays after the unshare syscall. Thus the task
> can/must detach from the existing undo list entries, too.
> 
> This fixes the kernel corruption, because it makes it impossible that
> undo records from two different namespaces are in sysvsem.undo_list.

So this was never an issue with clone(CLONE_NEWIPC|CLONE_SYSVSEM), which
should have had the same result as unshare(CLONE_NEWIPC&~CLONE_SYSVSEM)?

> I'm not sure who's the right maintainer, Andrew, could you merge it?
> 
> Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
> ---
>  kernel/fork.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 7f242b0..6f956a7 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1735,9 +1735,13 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
>  		goto bad_unshare_cleanup_semundo;
> 
>  	if (new_fs ||  new_mm || new_fd || new_ulist || new_nsproxy) {
> -		if (unshare_flags & CLONE_SYSVSEM) {
> +		if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM)) {
>  			/*
>  			 * CLONE_SYSVSEM is equivalent to sys_exit().
> +			 *
> +			 * CLONE_NEWIPC must also detach from the undolist: after switching
> +			 * to a new ipc namespace, the semaphore arrays from the old
> +			 * namespace are unreachable.
>  			 */
>  			exit_sem(current);
>  		}
> -- 
> 1.5.4.1
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