[PATCH net] rds: mark snapshot pages dirty in rds_info_getsockopt()

[PATCH net] rds: mark snapshot pages dirty in rds_info_getsockopt()

[Breno Leitao]

rds_info_getsockopt() pins the destination user pages with FOLL_WRITE and
the RDS_INFO_* producers memcpy the snapshot into them through
kmap_atomic(). Because that copy goes through the kernel direct map, the
dirty bit on the user PTE is never set, so unpin_user_pages() releases the
pages without marking them dirty. A file-backed destination page can then
be reclaimed without writeback, silently discarding the copied data.

Use unpin_user_pages_dirty_lock() with make_dirty=true so the modified
pages are marked dirty before they are unpinned.

Fixes: a8c879a7ee98 ("RDS: Info and stats")
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 net/rds/info.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rds/info.c b/net/rds/info.c
index f1b29994934a..17061f6ff74e 100644
--- a/net/rds/info.c
+++ b/net/rds/info.c
@@ -235,7 +235,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
 
 out:
 	if (pages)
-		unpin_user_pages(pages, nr_pages);
+		unpin_user_pages_dirty_lock(pages, nr_pages, true);
 	kfree(pages);
 
 	return ret;

---
base-commit: 9772589b57e44aedc240211c5c3f7a684a034d3a
change-id: 20260608-rds_fix-92d6c7f04fe2

Best regards,
-- 
Breno Leitao <leitao@debian.org>

Re: [PATCH net] rds: mark snapshot pages dirty in rds_info_getsockopt()

[Allison Henderson]

On Mon, 2026-06-08 at 02:32 -0700, Breno Leitao wrote:
> rds_info_getsockopt() pins the destination user pages with FOLL_WRITE and
> the RDS_INFO_* producers memcpy the snapshot into them through
> kmap_atomic(). Because that copy goes through the kernel direct map, the
> dirty bit on the user PTE is never set, so unpin_user_pages() releases the
> pages without marking them dirty. A file-backed destination page can then
> be reclaimed without writeback, silently discarding the copied data.
> 
> Use unpin_user_pages_dirty_lock() with make_dirty=true so the modified
> pages are marked dirty before they are unpinned.
> 
> Fixes: a8c879a7ee98 ("RDS: Info and stats")
> Signed-off-by: Breno Leitao <leitao@debian.org>
Hi Breno,

Thanks for adding the Fixes tag. One thing though: now that this is
standalone, it collides with "[PATCH net-next v3 2/2] rds: convert to
getsockopt_iter" since both rewrite the same unpin in the out: block of
rds_info_getsockopt().  

Easiest on everyone is to just keep it folded into the net-next series as
a three-patch set, rather than splitting the fix out to net.

With that, you can add my:
Reviewed-by: Allison Henderson <achender@kernel.org>

Thanks!
Allison


> ---
>  net/rds/info.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/rds/info.c b/net/rds/info.c
> index f1b29994934a..17061f6ff74e 100644
> --- a/net/rds/info.c
> +++ b/net/rds/info.c
> @@ -235,7 +235,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
>  
>  out:
>  	if (pages)
> -		unpin_user_pages(pages, nr_pages);
> +		unpin_user_pages_dirty_lock(pages, nr_pages, true);
>  	kfree(pages);
>  
>  	return ret;
> 
> ---
> base-commit: 9772589b57e44aedc240211c5c3f7a684a034d3a
> change-id: 20260608-rds_fix-92d6c7f04fe2
> 
> Best regards,

Re: [PATCH net] rds: mark snapshot pages dirty in rds_info_getsockopt()

[Breno Leitao]

On Tue, Jun 09, 2026 at 01:02:00AM -0700, Allison Henderson wrote:
> On Mon, 2026-06-08 at 02:32 -0700, Breno Leitao wrote:
> > rds_info_getsockopt() pins the destination user pages with FOLL_WRITE and
> > the RDS_INFO_* producers memcpy the snapshot into them through
> > kmap_atomic(). Because that copy goes through the kernel direct map, the
> > dirty bit on the user PTE is never set, so unpin_user_pages() releases the
> > pages without marking them dirty. A file-backed destination page can then
> > be reclaimed without writeback, silently discarding the copied data.
> > 
> > Use unpin_user_pages_dirty_lock() with make_dirty=true so the modified
> > pages are marked dirty before they are unpinned.
> > 
> > Fixes: a8c879a7ee98 ("RDS: Info and stats")
> > Signed-off-by: Breno Leitao <leitao@debian.org>
>
> Hi Breno,
> 
> Thanks for adding the Fixes tag. One thing though: now that this is
> standalone, it collides with "[PATCH net-next v3 2/2] rds: convert to
> getsockopt_iter" since both rewrite the same unpin in the out: block of
> rds_info_getsockopt().  
> 
> Easiest on everyone is to just keep it folded into the net-next series as
> a three-patch set, rather than splitting the fix out to net.

I got from the maintainers that they want to continue to split the fixes
into net and non fixes (features) into net-next.

	"So just prepare for net with Fixes tags and we'll route the
	patches accordingly." -- Jakub

https://lore.kernel.org/all/20260527155942.45c43c8d@kernel.org/

Thanks for the review,
--breno