Re: [PATCH v1 2/2] IB/core: don't disallow registering region starting at 0x0

[Yann Droneaud <ydroneaud@opteya.com>]

Hi,

Le mardi 14 avril 2015 à 12:20 +0300, Sagi Grimberg a écrit :
> On 4/13/2015 3:56 PM, Yann Droneaud wrote:
> > In a call to ib_umem_get(), if address is 0x0 and size is
> > already page aligned, check added in commit 8494057ab5e4
> > ("IB/uverbs: Prevent integer overflow in ib_umem_get address
> > arithmetic") will refuse to register a memory region that
> > could otherwise be valid (provided vm.mmap_min_addr sysctl
> > and mmap_low_allowed SELinux knobs allow userspace to map
> > something at address 0x0).
> >
> > This patch allows back such registration: ib_umem_get()
> > should probably don't care of the base address provided it
> > can be pinned with get_user_pages().
> >
> > There's two possible overflows, in (addr + size) and in
> > PAGE_ALIGN(addr + size), this patch keep ensuring none
> > of them happen while allowing to pin memory at address
> > 0x0. Anyway, the case of size equal 0 is no more (partially)
> > handled as 0-length memory region are disallowed by an
> > earlier check.
> >
> > Link: http://mid.gmane.org/cover.1428929103.git.ydroneaud@opteya.com
> > Cc: <stable@vger.kernel.org> # 8494057ab5e4 ("IB/uverbs: Prevent integer overflow in ib_umem_get address arithmetic")
> > Cc: Shachar Raindel <raindel@mellanox.com>
> > Cc: Jack Morgenstein <jackm@mellanox.com>
> > Cc: Or Gerlitz <ogerlitz@mellanox.com>
> > Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
> > ---
> >   drivers/infiniband/core/umem.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> > index 9ac4068d2088..38acb3cfc545 100644
> > --- a/drivers/infiniband/core/umem.c
> > +++ b/drivers/infiniband/core/umem.c
> > @@ -106,8 +106,8 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
> >   	 * If the combination of the addr and size requested for this memory
> >   	 * region causes an integer overflow, return error.
> >   	 */
> > -	if ((PAGE_ALIGN(addr + size) <= size) ||
> > -	    (PAGE_ALIGN(addr + size) <= addr))
> > +	if (((addr + size) < addr) ||
> > +	    PAGE_ALIGN(addr + size) < (addr + size))
> 
> If you do change the first statement to be: (addr + size) <= addr
> wouldn't it cover patch #1?
> 

Yes, but it doesn't sound a great place to do it: here it's about
overflow, so I'd prefer not doing the null memory region check there.

Regards.

-- 
Yann Droneaud
OPTEYA