linux-hardening - Re: [PATCH v1 1/2] mseal: fix mmap(FIXED) error code.

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Message-ID: <58e47a2e-6556-4a41-9fe5-1378f5257534@lucifer.local>
Date: Thu, 29 Aug 2024 13:09:41 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: jeffxu@...omium.org
Cc: akpm@...ux-foundation.org, linux-kselftest@...r.kernel.org,
        linux-mm@...ck.org, linux-hardening@...r.kernel.org,
        pedro.falcato@...il.com, rientjes@...gle.com, keescook@...omium.org,
        Liam Howlett <liam.howlett@...cle.com>, vbabka@...e.cz
Subject: Re: [PATCH v1 1/2] mseal: fix mmap(FIXED) error code.

Jeff... come on now.

Please cc- the reviewers of mm/mmap.c on these patches - that's me,
Vlastimil and Liam. Same for mm/vma.c, mm/vma.h, mm/vma_internal.h.

And it seems like it should be pretty obvious you should cc- Liam when it's
quite literally his code you're changing!

Relevant section from MAINTAINERS:

MEMORY MAPPING
M:	Andrew Morton <akpm@...ux-foundation.org>
R:	Liam R. Howlett <Liam.Howlett@...cle.com>
R:	Vlastimil Babka <vbabka@...e.cz>
R:	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
L:	linux-mm@...ck.org
S:	Maintained
W:	http://www.linux-mm.org
T:	git git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
F:	mm/mmap.c

On Wed, Aug 28, 2024 at 10:55:21PM GMT, jeffxu@...omium.org wrote:
> From: Jeff Xu <jeffxu@...omium.org>
>
> mmap(MAP_FIXED) should return EPERM when memory is sealed.
>
> Fixes: 4205a39e06da ("mm/munmap: replace can_modify_mm with can_modify_vma")
> Signed-off-by: Jeff Xu <jeffxu@...omium.org>
> ---
>  mm/mmap.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 80d70ed099cf..0cd0c0ef03c7 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1386,7 +1386,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>  		mt_on_stack(mt_detach);
>  		mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
>  		/* Prepare to unmap any existing mapping in the area */
> -		if (vms_gather_munmap_vmas(&vms, &mas_detach))
> +		error = vms_gather_munmap_vmas(&vms, &mas_detach);
> +		if (error == -EPERM)
> +			return -EPERM;
> +		if (error)
>  			return -ENOMEM;

Can't we just return the error here?

This is one for Liam, but I'm ostensibly in favour, this does seem valid!

>
>  		vmg.next = vms.next;
> --
> 2.46.0.295.g3b9ea8a38a-goog
>