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

[Steve French <smfrench@gmail.com>]

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