[PATCH 1/2] coda: fix reference counting in coda_file_mmap error path

[PATCH 1/2] coda: fix reference counting in coda_file_mmap error path

[Christian König]

mmap_region() now calls fput() on the vma->vm_file.

So we need to drop the extra reference on the coda file instead of the
host file.

Signed-off-by: Christian König <christian.koenig@amd.com>
Fixes: 1527f926fd04 ("mm: mmap: fix fput in error path v2")
CC: stable@vger.kernel.org # 5.11+
---
 fs/coda/file.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/coda/file.c b/fs/coda/file.c
index 128d63df5bfb..ef5ca22bfb3e 100644
--- a/fs/coda/file.c
+++ b/fs/coda/file.c
@@ -175,10 +175,10 @@ coda_file_mmap(struct file *coda_file, struct vm_area_struct *vma)
 	ret = call_mmap(vma->vm_file, vma);
 
 	if (ret) {
-		/* if call_mmap fails, our caller will put coda_file so we
-		 * should drop the reference to the host_file that we got.
+		/* if call_mmap fails, our caller will put host_file so we
+		 * should drop the reference to the coda_file that we got.
 		 */
-		fput(host_file);
+		fput(coda_file);
 		kfree(cvm_ops);
 	} else {
 		/* here we add redirects for the open/close vm_operations */
-- 
2.25.1

[PATCH 2/2] ovl: fix reference counting in ovl_mmap error path

[Christian König]

mmap_region() now calls fput() on the vma->vm_file.

Fix this by using vma_set_file() so it doesn't need to be
handled manually here any more.

Signed-off-by: Christian König <christian.koenig@amd.com>
Fixes: 1527f926fd04 ("mm: mmap: fix fput in error path v2")
CC: stable@vger.kernel.org # 5.11+
---
 fs/overlayfs/file.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index dbfb35fb0ff7..3847cdc069b5 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -430,20 +430,11 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 	if (WARN_ON(file != vma->vm_file))
 		return -EIO;
 
-	vma->vm_file = get_file(realfile);
+	vma_set_file(vma, realfile);
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	ret = call_mmap(vma->vm_file, vma);
 	revert_creds(old_cred);
-
-	if (ret) {
-		/* Drop reference count from new vm_file value */
-		fput(realfile);
-	} else {
-		/* Drop reference count from previous vm_file value */
-		fput(file);
-	}
-
 	ovl_file_accessed(file);
 
 	return ret;
-- 
2.25.1

Re: [PATCH 1/2] coda: fix reference counting in coda_file_mmap error path

[Daniel Vetter]

On Wed, Apr 21, 2021 at 03:20:11PM +0200, Christian König wrote:
> mmap_region() now calls fput() on the vma->vm_file.
> 
> So we need to drop the extra reference on the coda file instead of the
> host file.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> Fixes: 1527f926fd04 ("mm: mmap: fix fput in error path v2")
> CC: stable@vger.kernel.org # 5.11+

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  fs/coda/file.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/coda/file.c b/fs/coda/file.c
> index 128d63df5bfb..ef5ca22bfb3e 100644
> --- a/fs/coda/file.c
> +++ b/fs/coda/file.c
> @@ -175,10 +175,10 @@ coda_file_mmap(struct file *coda_file, struct vm_area_struct *vma)
>  	ret = call_mmap(vma->vm_file, vma);
>  
>  	if (ret) {
> -		/* if call_mmap fails, our caller will put coda_file so we
> -		 * should drop the reference to the host_file that we got.
> +		/* if call_mmap fails, our caller will put host_file so we
> +		 * should drop the reference to the coda_file that we got.
>  		 */
> -		fput(host_file);
> +		fput(coda_file);
>  		kfree(cvm_ops);
>  	} else {
>  		/* here we add redirects for the open/close vm_operations */
> -- 
> 2.25.1
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH 2/2] ovl: fix reference counting in ovl_mmap error path

[Daniel Vetter]

On Wed, Apr 21, 2021 at 03:20:12PM +0200, Christian König wrote:
> mmap_region() now calls fput() on the vma->vm_file.
> 
> Fix this by using vma_set_file() so it doesn't need to be
> handled manually here any more.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> Fixes: 1527f926fd04 ("mm: mmap: fix fput in error path v2")
> CC: stable@vger.kernel.org # 5.11+
> ---
>  fs/overlayfs/file.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index dbfb35fb0ff7..3847cdc069b5 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -430,20 +430,11 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
>  	if (WARN_ON(file != vma->vm_file))
>  		return -EIO;
>  
> -	vma->vm_file = get_file(realfile);
> +	vma_set_file(vma, realfile);

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

>  
>  	old_cred = ovl_override_creds(file_inode(file)->i_sb);
>  	ret = call_mmap(vma->vm_file, vma);
>  	revert_creds(old_cred);
> -
> -	if (ret) {
> -		/* Drop reference count from new vm_file value */
> -		fput(realfile);
> -	} else {
> -		/* Drop reference count from previous vm_file value */
> -		fput(file);
> -	}
> -
>  	ovl_file_accessed(file);
>  
>  	return ret;
> -- 
> 2.25.1
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH 1/2] coda: fix reference counting in coda_file_mmap error path

[Jan Harkes]

Looks good to me.

I'm also maintaining an out of tree coda module build that people sometimes use, which has workarounds for differences between the various kernel versions.

Do you have a reference to the corresponding mmap_region change? If it is merged already I'll probably be able to find it. Is this mmap_region change expected to be backported to any lts kernels?

Jan

On April 21, 2021 9:20:11 AM EDT, "Christian König" <ckoenig.leichtzumerken@gmail.com> wrote:
>mmap_region() now calls fput() on the vma->vm_file.
>
>So we need to drop the extra reference on the coda file instead of the
>host file.
>
>Signed-off-by: Christian König <christian.koenig@amd.com>
>Fixes: 1527f926fd04 ("mm: mmap: fix fput in error path v2")
>CC: stable@vger.kernel.org # 5.11+
>---
> fs/coda/file.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
>diff --git a/fs/coda/file.c b/fs/coda/file.c
>index 128d63df5bfb..ef5ca22bfb3e 100644
>--- a/fs/coda/file.c
>+++ b/fs/coda/file.c
>@@ -175,10 +175,10 @@ coda_file_mmap(struct file *coda_file, struct
>vm_area_struct *vma)
> 	ret = call_mmap(vma->vm_file, vma);
> 
> 	if (ret) {
>-		/* if call_mmap fails, our caller will put coda_file so we
>-		 * should drop the reference to the host_file that we got.
>+		/* if call_mmap fails, our caller will put host_file so we
>+		 * should drop the reference to the coda_file that we got.
> 		 */
>-		fput(host_file);
>+		fput(coda_file);
> 		kfree(cvm_ops);
> 	} else {
> 		/* here we add redirects for the open/close vm_operations */

Re: [PATCH 1/2] coda: fix reference counting in coda_file_mmap error path

[Christian König]

Hi Jan,

Am 22.04.21 um 14:27 schrieb Jan Harkes:
> Looks good to me.
>
> I'm also maintaining an out of tree coda module build that people sometimes use, which has workarounds for differences between the various kernel versions.
>
> Do you have a reference to the corresponding mmap_region change? If it is merged already I'll probably be able to find it. Is this mmap_region change expected to be backported to any lts kernels?

That is the following upstream commit in Linus tree:

commit 1527f926fd04490f648c42f42b45218a04754f87
Author: Christian König <christian.koenig@amd.com>
Date:   Fri Oct 9 15:08:55 2020 +0200

     mm: mmap: fix fput in error path v2

But I don't think we should backport that.

And sorry for the noise. We had so many places which expected different 
behavior that I didn't noticed that two occasions in the fs code 
actually rely on the current behavior.

For your out of tree module you could make the code version independent 
by setting the vma back to the original file in case of an error. That 
should work with both behaviors in mmap_region.

Thanks,
Christian.

>
> Jan
>
> On April 21, 2021 9:20:11 AM EDT, "Christian König" <ckoenig.leichtzumerken@gmail.com> wrote:
>> mmap_region() now calls fput() on the vma->vm_file.
>>
>> So we need to drop the extra reference on the coda file instead of the
>> host file.
>>
>> Signed-off-by: Christian König <christian.koenig@amd.com>
>> Fixes: 1527f926fd04 ("mm: mmap: fix fput in error path v2")
>> CC: stable@vger.kernel.org # 5.11+
>> ---
>> fs/coda/file.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/coda/file.c b/fs/coda/file.c
>> index 128d63df5bfb..ef5ca22bfb3e 100644
>> --- a/fs/coda/file.c
>> +++ b/fs/coda/file.c
>> @@ -175,10 +175,10 @@ coda_file_mmap(struct file *coda_file, struct
>> vm_area_struct *vma)
>> 	ret = call_mmap(vma->vm_file, vma);
>>
>> 	if (ret) {
>> -		/* if call_mmap fails, our caller will put coda_file so we
>> -		 * should drop the reference to the host_file that we got.
>> +		/* if call_mmap fails, our caller will put host_file so we
>> +		 * should drop the reference to the coda_file that we got.
>> 		 */
>> -		fput(host_file);
>> +		fput(coda_file);
>> 		kfree(cvm_ops);
>> 	} else {
>> 		/* here we add redirects for the open/close vm_operations */

Re: [PATCH 1/2] coda: fix reference counting in coda_file_mmap error path

[Jan Harkes]

On Thu, Apr 22, 2021 at 02:39:41PM +0200, Christian König wrote:
> Am 22.04.21 um 14:27 schrieb Jan Harkes:
> > Looks good to me.
> > 
> > I'm also maintaining an out of tree coda module build that people sometimes use, which has workarounds for differences between the various kernel versions.
> > 
> > Do you have a reference to the corresponding mmap_region change? If it is merged already I'll probably be able to find it. Is this mmap_region change expected to be backported to any lts kernels?
> 
> That is the following upstream commit in Linus tree:
> 
> commit 1527f926fd04490f648c42f42b45218a04754f87
> Author: Christian König <christian.koenig@amd.com>
> Date:   Fri Oct 9 15:08:55 2020 +0200
> 
>     mm: mmap: fix fput in error path v2
> 
> But I don't think we should backport that.
> 
> And sorry for the noise. We had so many places which expected different
> behavior that I didn't noticed that two occasions in the fs code actually
> rely on the current behavior.
> 
> For your out of tree module you could make the code version independent by
> setting the vma back to the original file in case of an error. That should
> work with both behaviors in mmap_region.

Awesome, I'll give that a try, it may very well be a cleaner solution
either way.

And thank you for following up after your original patch and finding
the filesystems that mess around with those mappings. I'm sure it would
have taken me a while to figure out why file refcounts would go weird
for some people, especially because this only happens in the error path.

Jan

Re: [PATCH 1/2] coda: fix reference counting in coda_file_mmap error path

[Christian König]

Am 22.04.21 um 15:51 schrieb Jan Harkes:
> On Thu, Apr 22, 2021 at 02:39:41PM +0200, Christian König wrote:
>> Am 22.04.21 um 14:27 schrieb Jan Harkes:
>>> Looks good to me.
>>>
>>> I'm also maintaining an out of tree coda module build that people sometimes use, which has workarounds for differences between the various kernel versions.
>>>
>>> Do you have a reference to the corresponding mmap_region change? If it is merged already I'll probably be able to find it. Is this mmap_region change expected to be backported to any lts kernels?
>> That is the following upstream commit in Linus tree:
>>
>> commit 1527f926fd04490f648c42f42b45218a04754f87
>> Author: Christian König <christian.koenig@amd.com>
>> Date:   Fri Oct 9 15:08:55 2020 +0200
>>
>>      mm: mmap: fix fput in error path v2
>>
>> But I don't think we should backport that.
>>
>> And sorry for the noise. We had so many places which expected different
>> behavior that I didn't noticed that two occasions in the fs code actually
>> rely on the current behavior.
>>
>> For your out of tree module you could make the code version independent by
>> setting the vma back to the original file in case of an error. That should
>> work with both behaviors in mmap_region.
> Awesome, I'll give that a try, it may very well be a cleaner solution
> either way.
>
> And thank you for following up after your original patch and finding
> the filesystems that mess around with those mappings. I'm sure it would
> have taken me a while to figure out why file refcounts would go weird
> for some people, especially because this only happens in the error path.

Kudos goes to Miklos for figured out why the refcount for overlayfs was 
suddenly wrong.

And please also see the follow up commit:

commit 295992fb815e791d14b18ef7cdbbaf1a76211a31 (able/vma_file)
Author: Christian König <christian.koenig@amd.com>
Date:   Mon Sep 14 15:09:33 2020 +0200

     mm: introduce vma_set_file function v5

It adds a new vma_set_file() function which implements the necessary 
refcount dance for changing the vma file in a clean manner.

Thanks,
Christian.

>
> Jan
>