From: "Christian König" <christian.koenig@amd.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: linux-fsdevel@vger.kernel.org, linux-mm <linux-mm@kvack.org>,
Chengguang Xu <cgxu519@mykernel.net>,
overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: [PATCH] ovl: fix mmap denywrite
Date: Mon, 12 Jul 2021 13:15:37 +0200 [thread overview]
Message-ID: <973a75b0-b3ba-9b5c-28a9-7854ec6d6db1@amd.com> (raw)
In-Reply-To: <YOhTrVWYi1aFY3o0@miu.piliscsaba.redhat.com>
Am 09.07.21 um 15:48 schrieb Miklos Szeredi:
> On Wed, Jun 23, 2021 at 01:41:02PM +0200, Christian König wrote:
>>
>> Am 22.06.21 um 17:10 schrieb Miklos Szeredi:
>>> On Tue, 22 Jun 2021 at 14:43, Christian König <christian.koenig@amd.com> wrote:
>>>> Am 22.06.21 um 14:30 schrieb Miklos Szeredi:
>>>>> Overlayfs did not honor positive i_writecount on realfile for VM_DENYWRITE
>>>>> mappings. Similarly negative i_mmap_writable counts were ignored for
>>>>> VM_SHARED mappings.
>>>>>
>>>>> Fix by making vma_set_file() switch the temporary counts obtained and
>>>>> released by mmap_region().
>>>> Mhm, I don't fully understand the background but that looks like
>>>> something specific to overlayfs to me.
>>>>
>>>> So why are you changing the common helper?
>>> Need to hold the temporary counts until the final ones are obtained in
>>> vma_link(), which is out of overlayfs' scope.
>> Ah! So basically we need to move the denial counts which mmap_region() added
>> to the original file to the new one as well. That's indeed a rather good
>> point.
>>
>> Can you rather change the vma_set_file() function to return the error and
>> add a __must_check?
>>
>> I can take care fixing the users in DMA-buf and DRM subsystem.
> Okay, but changing to __must_check has to be the last step to avoid compile
> errors. This v2 is with __must_check commented out.
Good point. Please ping me whenever that is upstream and I will take
care of fixing all the callers in the DRM subsystem and DMA-buf
>
> Thanks,
> Miklos
> ---
>
> From: Miklos Szeredi <mszeredi@redhat.com>
> Subject: [PATCH v2] ovl: fix mmap denywrite
>
> Overlayfs did not honor positive i_writecount on realfile for VM_DENYWRITE
> mappings. Similarly negative i_mmap_writable counts were ignored for
> VM_SHARED mappings.
>
> Fix by making vma_set_file() switch the temporary counts obtained and
> released by mmap_region().
>
> Reported-by: Chengguang Xu <cgxu519@mykernel.net>
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Regards,
Christian.
> ---
> fs/overlayfs/file.c | 4 +++-
> include/linux/mm.h | 2 +-
> mm/mmap.c | 2 +-
> mm/util.c | 27 ++++++++++++++++++++++++++-
> 4 files changed, 31 insertions(+), 4 deletions(-)
>
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -430,7 +430,9 @@ static int ovl_mmap(struct file *file, s
> if (WARN_ON(file != vma->vm_file))
> return -EIO;
>
> - vma_set_file(vma, realfile);
> + ret = vma_set_file(vma, realfile);
> + if (ret)
> + return ret;
>
> old_cred = ovl_override_creds(file_inode(file)->i_sb);
> ret = call_mmap(vma->vm_file, vma);
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2776,7 +2776,7 @@ static inline void vma_set_page_prot(str
> }
> #endif
>
> -void vma_set_file(struct vm_area_struct *vma, struct file *file);
> +int /* __must_check */ vma_set_file(struct vm_area_struct *vma, struct file *file);
>
> #ifdef CONFIG_NUMA_BALANCING
> unsigned long change_prot_numa(struct vm_area_struct *vma,
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1807,6 +1807,7 @@ unsigned long mmap_region(struct file *f
> */
> vma->vm_file = get_file(file);
> error = call_mmap(file, vma);
> + file = vma->vm_file;
> if (error)
> goto unmap_and_free_vma;
>
> @@ -1868,7 +1869,6 @@ unsigned long mmap_region(struct file *f
> if (vm_flags & VM_DENYWRITE)
> allow_write_access(file);
> }
> - file = vma->vm_file;
> out:
> perf_event_mmap(vma);
>
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -314,12 +314,37 @@ int vma_is_stack_for_current(struct vm_a
> /*
> * Change backing file, only valid to use during initial VMA setup.
> */
> -void vma_set_file(struct vm_area_struct *vma, struct file *file)
> +int vma_set_file(struct vm_area_struct *vma, struct file *file)
> {
> + vm_flags_t vm_flags = vma->vm_flags;
> + int err = 0;
> +
> /* Changing an anonymous vma with this is illegal */
> get_file(file);
> +
> + /* Get temporary denial counts on replacement */
> + if (vm_flags & VM_DENYWRITE) {
> + err = deny_write_access(file);
> + if (err)
> + goto out_put;
> + }
> + if (vm_flags & VM_SHARED) {
> + err = mapping_map_writable(file->f_mapping);
> + if (err)
> + goto out_allow;
> + }
> +
> swap(vma->vm_file, file);
> +
> + /* Undo temporary denial counts on replaced */
> + if (vm_flags & VM_SHARED)
> + mapping_unmap_writable(file->f_mapping);
> +out_allow:
> + if (vm_flags & VM_DENYWRITE)
> + allow_write_access(file);
> +out_put:
> fput(file);
> + return err;
> }
> EXPORT_SYMBOL(vma_set_file);
>
next prev parent reply other threads:[~2021-07-12 11:18 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-22 12:30 [PATCH] ovl: fix mmap denywrite Miklos Szeredi
2021-06-22 12:43 ` Christian König
2021-06-22 15:10 ` Miklos Szeredi
2021-06-23 11:41 ` Christian König
2021-07-09 13:48 ` Miklos Szeredi
2021-07-12 11:15 ` Christian König [this message]
2021-06-23 6:06 ` 回复:[PATCH] " Chengguang Xu
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