[PATCH] mm: respect arch_dup_mmap() return value

[PATCH] mm: respect arch_dup_mmap() return value

[Nadav Amit]

Commit d70f2a14b72a4 ("include/linux/sched/mm.h: uninline
mmdrop_async(), etc") ignored the return value of arch_dup_mmap(). As a
result, on x86, a failure to duplicate the LDT (e.g., due to memory
allocation error), would leave the duplicated memory mapping in an
inconsistent state.

Fix by regarding the return value, as it was before the change.

Fixes: d70f2a14b72a4 ("include/linux/sched/mm.h: uninline mmdrop_async(), etc")
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 kernel/fork.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 1b27babc4c78..4527d1d331de 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -549,8 +549,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
 			goto out;
 	}
 	/* a new mm has just been created */
-	arch_dup_mmap(oldmm, mm);
-	retval = 0;
+	retval = arch_dup_mmap(oldmm, mm);
 out:
 	up_write(&mm->mmap_sem);
 	flush_tlb_mm(oldmm);
-- 
2.17.1

Re: [PATCH] mm: respect arch_dup_mmap() return value

[Michal Hocko]

On Wed 22-08-18 22:12:29, Nadav Amit wrote:
> Commit d70f2a14b72a4 ("include/linux/sched/mm.h: uninline
> mmdrop_async(), etc") ignored the return value of arch_dup_mmap(). As a
> result, on x86, a failure to duplicate the LDT (e.g., due to memory
> allocation error), would leave the duplicated memory mapping in an
> inconsistent state.
> 
> Fix by regarding the return value, as it was before the change.

Ohh, well spotted! I have a vague recollection I didn't really like the
patch. For other reasons. I didn't get to review it properly back then
because I didn't have much time and I didn't have a high motivation
because I simple disagreed with the patch.

> Fixes: d70f2a14b72a4 ("include/linux/sched/mm.h: uninline mmdrop_async(), etc")
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: Nadav Amit <namit@vmware.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  kernel/fork.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 1b27babc4c78..4527d1d331de 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -549,8 +549,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
>  			goto out;
>  	}
>  	/* a new mm has just been created */
> -	arch_dup_mmap(oldmm, mm);
> -	retval = 0;
> +	retval = arch_dup_mmap(oldmm, mm);
>  out:
>  	up_write(&mm->mmap_sem);
>  	flush_tlb_mm(oldmm);
> -- 
> 2.17.1
> 

-- 
Michal Hocko
SUSE Labs