[PATCH] cifs: Fix the smbd_request and smbd_reponse slabs to allow usercopy

[PATCH] cifs: Fix the smbd_request and smbd_reponse slabs to allow usercopy

[David Howells]

The handling of received data in the smbdirect client code involves using
copy_to_iter() to copy data from the smbd_reponse struct's packet trailer
to a folioq buffer provided by netfslib that encapsulates a chunk of
pagecache.

If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks
then performed in copy_to_iter() oopsing with something like the following:

 CIFS: Attempting to mount //172.31.9.1/test
 CIFS: VFS: RDMA transport established
 usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)!
 ------------[ cut here ]------------
 kernel BUG at mm/usercopy.c:102!
 ...
 RIP: 0010:usercopy_abort+0x6c/0x80
 ...
 Call Trace:
  <TASK>
  __check_heap_object+0xe3/0x120
  __check_object_size+0x4dc/0x6d0
  smbd_recv+0x77f/0xfe0 [cifs]
  cifs_readv_from_socket+0x276/0x8f0 [cifs]
  cifs_read_from_socket+0xcd/0x120 [cifs]
  cifs_demultiplex_thread+0x7e9/0x2d50 [cifs]
  kthread+0x396/0x830
  ret_from_fork+0x2b8/0x3b0
  ret_from_fork_asm+0x1a/0x30

The problem is that the smbd_response slab's packet field isn't marked as
being permitted for usercopy.

Fix this by passing parameters to kmem_slab_create() to indicate that
copy_to_iter() is permitted from the packet region of the smbd_response
slab objects.

Further, do the same thing for smbd_request slab objects and their packet
field.

Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
Reported-by: Stefan Metzmacher <metze@samba.org>
Link: https://lore.kernel.org/r/acb7f612-df26-4e2a-a35d-7cd040f513e1@samba.org/
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <stfrench@microsoft.com>
cc: Paulo Alcantara <pc@manguebit.com>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/smb/client/smbdirect.c |   21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
index ef6bf8d6808d..5915273636ad 100644
--- a/fs/smb/client/smbdirect.c
+++ b/fs/smb/client/smbdirect.c
@@ -1476,12 +1476,17 @@ static int allocate_caches_and_workqueue(struct smbd_connection *info)
 	int rc;
 
 	scnprintf(name, MAX_NAME_LEN, "smbd_request_%p", info);
+	struct kmem_cache_args request_args = {
+		.align		= __alignof__(struct smbd_request),
+		.useroffset	= offsetof(struct smbd_request, packet),
+		.usersize	= sizeof(struct smbdirect_data_transfer),
+	};
 	info->request_cache =
 		kmem_cache_create(
 			name,
 			sizeof(struct smbd_request) +
 				sizeof(struct smbdirect_data_transfer),
-			0, SLAB_HWCACHE_ALIGN, NULL);
+			&request_args, SLAB_HWCACHE_ALIGN);
 	if (!info->request_cache)
 		return -ENOMEM;
 
@@ -1492,12 +1497,16 @@ static int allocate_caches_and_workqueue(struct smbd_connection *info)
 		goto out1;
 
 	scnprintf(name, MAX_NAME_LEN, "smbd_response_%p", info);
+
+	struct kmem_cache_args response_args = {
+		.align		= __alignof__(struct smbd_response),
+		.useroffset	= offsetof(struct smbd_response, packet),
+		.usersize	= sp->max_recv_size,
+	};
 	info->response_cache =
-		kmem_cache_create(
-			name,
-			sizeof(struct smbd_response) +
-				sp->max_recv_size,
-			0, SLAB_HWCACHE_ALIGN, NULL);
+		kmem_cache_create(name,
+				  sizeof(struct smbd_response) + sp->max_recv_size,
+				  &response_args, SLAB_HWCACHE_ALIGN);
 	if (!info->response_cache)
 		goto out2;
 

Re: [PATCH] cifs: Fix the smbd_request and smbd_reponse slabs to allow usercopy

[Stefan Metzmacher]

Am 25.06.25 um 15:37 schrieb David Howells:
> The handling of received data in the smbdirect client code involves using
> copy_to_iter() to copy data from the smbd_reponse struct's packet trailer
> to a folioq buffer provided by netfslib that encapsulates a chunk of
> pagecache.
> 
> If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks
> then performed in copy_to_iter() oopsing with something like the following:
> 
>   CIFS: Attempting to mount //172.31.9.1/test
>   CIFS: VFS: RDMA transport established
>   usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)!
>   ------------[ cut here ]------------
>   kernel BUG at mm/usercopy.c:102!
>   ...
>   RIP: 0010:usercopy_abort+0x6c/0x80
>   ...
>   Call Trace:
>    <TASK>
>    __check_heap_object+0xe3/0x120
>    __check_object_size+0x4dc/0x6d0
>    smbd_recv+0x77f/0xfe0 [cifs]
>    cifs_readv_from_socket+0x276/0x8f0 [cifs]
>    cifs_read_from_socket+0xcd/0x120 [cifs]
>    cifs_demultiplex_thread+0x7e9/0x2d50 [cifs]
>    kthread+0x396/0x830
>    ret_from_fork+0x2b8/0x3b0
>    ret_from_fork_asm+0x1a/0x30
> 
> The problem is that the smbd_response slab's packet field isn't marked as
> being permitted for usercopy.
> 
> Fix this by passing parameters to kmem_slab_create() to indicate that
> copy_to_iter() is permitted from the packet region of the smbd_response
> slab objects.
> 
> Further, do the same thing for smbd_request slab objects and their packet
> field.
> 
> Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
> Reported-by: Stefan Metzmacher <metze@samba.org>
> Link: https://lore.kernel.org/r/acb7f612-df26-4e2a-a35d-7cd040f513e1@samba.org/
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Steve French <stfrench@microsoft.com>
> cc: Paulo Alcantara <pc@manguebit.com>
> cc: linux-cifs@vger.kernel.org
> cc: netfs@lists.linux.dev
> cc: linux-fsdevel@vger.kernel.org
> ---
>   fs/smb/client/smbdirect.c |   21 +++++++++++++++------
>   1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
> index ef6bf8d6808d..5915273636ad 100644
> --- a/fs/smb/client/smbdirect.c
> +++ b/fs/smb/client/smbdirect.c
> @@ -1476,12 +1476,17 @@ static int allocate_caches_and_workqueue(struct smbd_connection *info)
>   	int rc;
>   
>   	scnprintf(name, MAX_NAME_LEN, "smbd_request_%p", info);
> +	struct kmem_cache_args request_args = {
> +		.align		= __alignof__(struct smbd_request),
> +		.useroffset	= offsetof(struct smbd_request, packet),
> +		.usersize	= sizeof(struct smbdirect_data_transfer),

This looks wrong, the smbdirect_data_transfer header itself
should be written by userspace.

So I guess we don't need this at all.

> +	};
>   	info->request_cache =
>   		kmem_cache_create(
>   			name,
>   			sizeof(struct smbd_request) +
>   				sizeof(struct smbdirect_data_transfer),
> -			0, SLAB_HWCACHE_ALIGN, NULL);
> +			&request_args, SLAB_HWCACHE_ALIGN);
>   	if (!info->request_cache)
>   		return -ENOMEM;
>   
> @@ -1492,12 +1497,16 @@ static int allocate_caches_and_workqueue(struct smbd_connection *info)
>   		goto out1;
>   
>   	scnprintf(name, MAX_NAME_LEN, "smbd_response_%p", info);
> +
> +	struct kmem_cache_args response_args = {
> +		.align		= __alignof__(struct smbd_response),
> +		.useroffset	= offsetof(struct smbd_response, packet),
> +		.usersize	= sp->max_recv_size,

This should be have + sizeof(struct smbdirect_data_transfer) for useroffset
and - sizeof(struct smbdirect_data_transfer) for usersize

As the smbdirect_data_transfer header should not accessed by userspace.

My attempt looks like this:

-               kmem_cache_create(
+               kmem_cache_create_usercopy(
                         name,
                         sizeof(struct smbd_response) +
                                 sp->max_recv_size,
-                       0, SLAB_HWCACHE_ALIGN, NULL);
+                       __alignof__(struct smbd_response),
+                       SLAB_HWCACHE_ALIGN,
+                       /*
+                        * only the payload should be exposed
+                        */
+                       offsetof(struct smbd_response, packet) +
+                                sizeof(struct smbdirect_data_transfer),
+                       sp->max_recv_size -
+                               sizeof(struct smbdirect_data_transfer),
+                       NULL);

But I noticed that kmem_cache_create_usercopy is a legacy wrapper.

[PATCH v2] cifs: Fix the smbd_request and smbd_reponse slabs to allow usercopy

[David Howells]

    
The handling of received data in the smbdirect client code involves using
copy_to_iter() to copy data from the smbd_reponse struct's packet trailer
to a folioq buffer provided by netfslib that encapsulates a chunk of
pagecache.

If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks
then performed in copy_to_iter() oopsing with something like the following:

 CIFS: Attempting to mount //172.31.9.1/test
 CIFS: VFS: RDMA transport established
 usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)!
 ------------[ cut here ]------------
 kernel BUG at mm/usercopy.c:102!
 ...
 RIP: 0010:usercopy_abort+0x6c/0x80
 ...
 Call Trace:
  <TASK>
  __check_heap_object+0xe3/0x120
  __check_object_size+0x4dc/0x6d0
  smbd_recv+0x77f/0xfe0 [cifs]
  cifs_readv_from_socket+0x276/0x8f0 [cifs]
  cifs_read_from_socket+0xcd/0x120 [cifs]
  cifs_demultiplex_thread+0x7e9/0x2d50 [cifs]
  kthread+0x396/0x830
  ret_from_fork+0x2b8/0x3b0
  ret_from_fork_asm+0x1a/0x30

The problem is that the smbd_response slab's packet field isn't marked as
being permitted for usercopy.

Fix this by passing parameters to kmem_slab_create() to indicate that
copy_to_iter() is permitted from the packet region of the smbd_response
slab objects, less the header space.

Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
Reported-by: Stefan Metzmacher <metze@samba.org>
Link: https://lore.kernel.org/r/acb7f612-df26-4e2a-a35d-7cd040f513e1@samba.org/
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <stfrench@microsoft.com>
cc: Paulo Alcantara <pc@manguebit.com>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/smb/client/smbdirect.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
index ef6bf8d6808d..f9773cc0d562 100644
--- a/fs/smb/client/smbdirect.c
+++ b/fs/smb/client/smbdirect.c
@@ -1475,6 +1475,9 @@ static int allocate_caches_and_workqueue(struct smbd_connection *info)
 	char name[MAX_NAME_LEN];
 	int rc;
 
+	if (WARN_ON_ONCE(sp->max_recv_size < sizeof(struct smbdirect_data_transfer)))
+		return -ENOMEM;
+
 	scnprintf(name, MAX_NAME_LEN, "smbd_request_%p", info);
 	info->request_cache =
 		kmem_cache_create(
@@ -1492,12 +1495,17 @@ static int allocate_caches_and_workqueue(struct smbd_connection *info)
 		goto out1;
 
 	scnprintf(name, MAX_NAME_LEN, "smbd_response_%p", info);
+
+	struct kmem_cache_args response_args = {
+		.align		= __alignof__(struct smbd_response),
+		.useroffset	= (offsetof(struct smbd_response, packet) +
+				   sizeof(struct smbdirect_data_transfer)),
+		.usersize	= sp->max_recv_size - sizeof(struct smbdirect_data_transfer),
+	};
 	info->response_cache =
-		kmem_cache_create(
-			name,
-			sizeof(struct smbd_response) +
-				sp->max_recv_size,
-			0, SLAB_HWCACHE_ALIGN, NULL);
+		kmem_cache_create(name,
+				  sizeof(struct smbd_response) + sp->max_recv_size,
+				  &response_args, SLAB_HWCACHE_ALIGN);
 	if (!info->response_cache)
 		goto out2;
 

Re: [PATCH v2] cifs: Fix the smbd_request and smbd_reponse slabs to allow usercopy

[Stefan Metzmacher]

reviewed-by and tested-by: Stefan Metzmacher <metze@samba.org>

Am 25.06.25 um 16:46 schrieb David Howells:
>      
> The handling of received data in the smbdirect client code involves using
> copy_to_iter() to copy data from the smbd_reponse struct's packet trailer
> to a folioq buffer provided by netfslib that encapsulates a chunk of
> pagecache.
> 
> If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks
> then performed in copy_to_iter() oopsing with something like the following:
> 
>   CIFS: Attempting to mount //172.31.9.1/test
>   CIFS: VFS: RDMA transport established
>   usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)!
>   ------------[ cut here ]------------
>   kernel BUG at mm/usercopy.c:102!
>   ...
>   RIP: 0010:usercopy_abort+0x6c/0x80
>   ...
>   Call Trace:
>    <TASK>
>    __check_heap_object+0xe3/0x120
>    __check_object_size+0x4dc/0x6d0
>    smbd_recv+0x77f/0xfe0 [cifs]
>    cifs_readv_from_socket+0x276/0x8f0 [cifs]
>    cifs_read_from_socket+0xcd/0x120 [cifs]
>    cifs_demultiplex_thread+0x7e9/0x2d50 [cifs]
>    kthread+0x396/0x830
>    ret_from_fork+0x2b8/0x3b0
>    ret_from_fork_asm+0x1a/0x30
> 
> The problem is that the smbd_response slab's packet field isn't marked as
> being permitted for usercopy.
> 
> Fix this by passing parameters to kmem_slab_create() to indicate that
> copy_to_iter() is permitted from the packet region of the smbd_response
> slab objects, less the header space.
> 
> Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
> Reported-by: Stefan Metzmacher <metze@samba.org>
> Link: https://lore.kernel.org/r/acb7f612-df26-4e2a-a35d-7cd040f513e1@samba.org/
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Steve French <stfrench@microsoft.com>
> cc: Paulo Alcantara <pc@manguebit.com>
> cc: linux-cifs@vger.kernel.org
> cc: netfs@lists.linux.dev
> cc: linux-fsdevel@vger.kernel.org
> ---
>   fs/smb/client/smbdirect.c |   18 +++++++++++++-----
>   1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
> index ef6bf8d6808d..f9773cc0d562 100644
> --- a/fs/smb/client/smbdirect.c
> +++ b/fs/smb/client/smbdirect.c
> @@ -1475,6 +1475,9 @@ static int allocate_caches_and_workqueue(struct smbd_connection *info)
>   	char name[MAX_NAME_LEN];
>   	int rc;
>   
> +	if (WARN_ON_ONCE(sp->max_recv_size < sizeof(struct smbdirect_data_transfer)))
> +		return -ENOMEM;
> +
>   	scnprintf(name, MAX_NAME_LEN, "smbd_request_%p", info);
>   	info->request_cache =
>   		kmem_cache_create(
> @@ -1492,12 +1495,17 @@ static int allocate_caches_and_workqueue(struct smbd_connection *info)
>   		goto out1;
>   
>   	scnprintf(name, MAX_NAME_LEN, "smbd_response_%p", info);
> +
> +	struct kmem_cache_args response_args = {
> +		.align		= __alignof__(struct smbd_response),
> +		.useroffset	= (offsetof(struct smbd_response, packet) +
> +				   sizeof(struct smbdirect_data_transfer)),
> +		.usersize	= sp->max_recv_size - sizeof(struct smbdirect_data_transfer),
> +	};
>   	info->response_cache =
> -		kmem_cache_create(
> -			name,
> -			sizeof(struct smbd_response) +
> -				sp->max_recv_size,
> -			0, SLAB_HWCACHE_ALIGN, NULL);
> +		kmem_cache_create(name,
> +				  sizeof(struct smbd_response) + sp->max_recv_size,
> +				  &response_args, SLAB_HWCACHE_ALIGN);
>   	if (!info->response_cache)
>   		goto out2;
>   

Re: [PATCH v2] cifs: Fix the smbd_request and smbd_reponse slabs to allow usercopy

[Steve French]

added to cifs-2.6.git for-next and added RB and tested-by

On Wed, Jun 25, 2025 at 10:55 AM Stefan Metzmacher <metze@samba.org> wrote:
>
> reviewed-by and tested-by: Stefan Metzmacher <metze@samba.org>
>
> Am 25.06.25 um 16:46 schrieb David Howells:
> >
> > The handling of received data in the smbdirect client code involves using
> > copy_to_iter() to copy data from the smbd_reponse struct's packet trailer
> > to a folioq buffer provided by netfslib that encapsulates a chunk of
> > pagecache.
> >
> > If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks
> > then performed in copy_to_iter() oopsing with something like the following:
> >
> >   CIFS: Attempting to mount //172.31.9.1/test
> >   CIFS: VFS: RDMA transport established
> >   usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)!
> >   ------------[ cut here ]------------
> >   kernel BUG at mm/usercopy.c:102!
> >   ...
> >   RIP: 0010:usercopy_abort+0x6c/0x80
> >   ...
> >   Call Trace:
> >    <TASK>
> >    __check_heap_object+0xe3/0x120
> >    __check_object_size+0x4dc/0x6d0
> >    smbd_recv+0x77f/0xfe0 [cifs]
> >    cifs_readv_from_socket+0x276/0x8f0 [cifs]
> >    cifs_read_from_socket+0xcd/0x120 [cifs]
> >    cifs_demultiplex_thread+0x7e9/0x2d50 [cifs]
> >    kthread+0x396/0x830
> >    ret_from_fork+0x2b8/0x3b0
> >    ret_from_fork_asm+0x1a/0x30
> >
> > The problem is that the smbd_response slab's packet field isn't marked as
> > being permitted for usercopy.
> >
> > Fix this by passing parameters to kmem_slab_create() to indicate that
> > copy_to_iter() is permitted from the packet region of the smbd_response
> > slab objects, less the header space.
> >
> > Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
> > Reported-by: Stefan Metzmacher <metze@samba.org>
> > Link: https://lore.kernel.org/r/acb7f612-df26-4e2a-a35d-7cd040f513e1@samba.org/
> > Signed-off-by: David Howells <dhowells@redhat.com>
> > cc: Steve French <stfrench@microsoft.com>
> > cc: Paulo Alcantara <pc@manguebit.com>
> > cc: linux-cifs@vger.kernel.org
> > cc: netfs@lists.linux.dev
> > cc: linux-fsdevel@vger.kernel.org
> > ---
> >   fs/smb/client/smbdirect.c |   18 +++++++++++++-----
> >   1 file changed, 13 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
> > index ef6bf8d6808d..f9773cc0d562 100644
> > --- a/fs/smb/client/smbdirect.c
> > +++ b/fs/smb/client/smbdirect.c
> > @@ -1475,6 +1475,9 @@ static int allocate_caches_and_workqueue(struct smbd_connection *info)
> >       char name[MAX_NAME_LEN];
> >       int rc;
> >
> > +     if (WARN_ON_ONCE(sp->max_recv_size < sizeof(struct smbdirect_data_transfer)))
> > +             return -ENOMEM;
> > +
> >       scnprintf(name, MAX_NAME_LEN, "smbd_request_%p", info);
> >       info->request_cache =
> >               kmem_cache_create(
> > @@ -1492,12 +1495,17 @@ static int allocate_caches_and_workqueue(struct smbd_connection *info)
> >               goto out1;
> >
> >       scnprintf(name, MAX_NAME_LEN, "smbd_response_%p", info);
> > +
> > +     struct kmem_cache_args response_args = {
> > +             .align          = __alignof__(struct smbd_response),
> > +             .useroffset     = (offsetof(struct smbd_response, packet) +
> > +                                sizeof(struct smbdirect_data_transfer)),
> > +             .usersize       = sp->max_recv_size - sizeof(struct smbdirect_data_transfer),
> > +     };
> >       info->response_cache =
> > -             kmem_cache_create(
> > -                     name,
> > -                     sizeof(struct smbd_response) +
> > -                             sp->max_recv_size,
> > -                     0, SLAB_HWCACHE_ALIGN, NULL);
> > +             kmem_cache_create(name,
> > +                               sizeof(struct smbd_response) + sp->max_recv_size,
> > +                               &response_args, SLAB_HWCACHE_ALIGN);
> >       if (!info->response_cache)
> >               goto out2;
> >
>
>


-- 
Thanks,

Steve