linux-kernel - Re: [PATCH next] mm/maps: move kmalloc() call location in do_procmap

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Message-ID: <693725d9-a293-414f-a706-f77446e335b1@redhat.com>
Date: Wed, 2 Jul 2025 16:44:01 +0200
From: David Hildenbrand <david@...hat.com>
To: Jeongjun Park <aha310510@...il.com>, akpm@...ux-foundation.org
Cc: andrii@...nel.org, osalvador@...e.de, Liam.Howlett@...cle.com,
 surenb@...gle.com, christophe.leroy@...roup.eu,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 syzbot+6246a83e7bd9f8a3e239@...kaller.appspotmail.com
Subject: Re: [PATCH next] mm/maps: move kmalloc() call location in
 do_procmap_query() out of RCU critical section

On 02.07.25 15:53, Jeongjun Park wrote:
> In do_procmap_query(), we are allocating name_buf as much as name_buf_sz
> with kmalloc().
> 
> However, due to the previous commit eff061546ca5
> ("mm/maps: execute PROCMAP_QUERY ioctl under per-vma locks"),
> the location of kmalloc() is located inside the RCU critical section.
> 
> This causes might_sleep_if() to be called inside the RCU critical section,
> so we need to move the call location of kmalloc() outside the RCU critical
> section to prevent this.
> 
> Reported-by: syzbot+6246a83e7bd9f8a3e239@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=6246a83e7bd9f8a3e239
> Fixes: eff061546ca5 ("mm/maps: execute PROCMAP_QUERY ioctl under per-vma locks")

That commit is not upstream yet (and the commit id is not stable), so it 
should be squashed into the problematic commit.

As a side note: the patch subject of this and the original patch should 
start with "fs/proc/task_mmu", not "mm/maps".

-- 
Cheers,

David / dhildenb