[PATCH 3.2 044/164] IB/core: don't disallow registering region starting at 0x0

[Ben Hutchings]

3.2.70-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Yann Droneaud <ydroneaud@xxxxxxxxxx>

commit 66578b0b2f69659f00b6169e6fe7377c4b100d18 upstream.

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@xxxxxxxxxx
Cc: Shachar Raindel <raindel@xxxxxxxxxxxx>
Cc: Jack Morgenstein <jackm@xxxxxxxxxxxx>
Cc: Or Gerlitz <ogerlitz@xxxxxxxxxxxx>
Signed-off-by: Yann Droneaud <ydroneaud@xxxxxxxxxx>
Reviewed-by: Sagi Grimberg <sagig@xxxxxxxxxxxx>
Reviewed-by: Haggai Eran <haggaie@xxxxxxxxxxxx>
Signed-off-by: Doug Ledford <dledford@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/infiniband/core/umem.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -101,8 +101,8 @@ struct ib_umem *ib_umem_get(struct ib_uc
 	 * 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))
 		return ERR_PTR(-EINVAL);
 
 	if (!can_do_mlock())

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