Re: [PATCH v2 1/2] mm/ksm: fix ksm exec support for prctl

[David Hildenbrand <david@redhat.com>]

On 22.03.24 07:09, Jinjiang Tu wrote:
> commit 3c6f33b7273a ("mm/ksm: support fork/exec for prctl") inherits
> MMF_VM_MERGE_ANY flag when a task calls execve(). Howerver, it doesn't
> create the mm_slot, so ksmd will not try to scan this task.
> 
> To fix it, allocate and add the mm_slot to ksm_mm_head in __bprm_mm_init()
> when the mm has MMF_VM_MERGE_ANY flag.
> 
> Fixes: 3c6f33b7273a ("mm/ksm: support fork/exec for prctl")
> Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
> ---
>   fs/exec.c           | 10 ++++++++++
>   include/linux/ksm.h | 13 +++++++++++++
>   2 files changed, 23 insertions(+)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index ff6f26671cfc..66202d016a0a 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -67,6 +67,7 @@
>   #include <linux/time_namespace.h>
>   #include <linux/user_events.h>
>   #include <linux/rseq.h>
> +#include <linux/ksm.h>
>   
>   #include <linux/uaccess.h>
>   #include <asm/mmu_context.h>
> @@ -267,6 +268,13 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
>   		goto err_free;
>   	}
>   
> +	/*
> +	 * Need to be called with mmap write lock
> +	 * held, to avoid race with ksmd.
> +	*/
> +	if (ksm_execve(mm))
> +		goto err_ksm;
> +

But now, would we revert what insert_vm_struct() did?

We're freeing the VMA later, but we might have accounted memory.


What would be cleaner is doing the ksm_execve() before the 
insert_vm_struct(), and then cleaning up in case insert_vm_struct() failed.

-- 
Cheers,

David / dhildenb