[PATCH 3.4 22/43] IB/nes: Return an error on ib_copy_from_udata() failure instead of NULL

[Greg Kroah-Hartman]

3.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Yann Droneaud <ydroneaud@xxxxxxxxxx>

commit 9d194d1025f463392feafa26ff8c2d8247f71be1 upstream.

In case of error while accessing to userspace memory, function
nes_create_qp() returns NULL instead of an error code wrapped through
ERR_PTR().  But NULL is not expected by ib_uverbs_create_qp(), as it
check for error with IS_ERR().

As page 0 is likely not mapped, it is going to trigger an Oops when
the kernel will try to dereference NULL pointer to access to struct
ib_qp's fields.

In some rare cases, page 0 could be mapped by userspace, which could
turn this bug to a vulnerability that could be exploited: the function
pointers in struct ib_device will be under userspace total control.

This was caught when using spatch (aka. coccinelle)
to rewrite calls to ib_copy_{from,to}_udata().

Link: https://www.gitorious.org/opteya/ib-hw-nes-create-qp-null
Link: https://www.gitorious.org/opteya/coccib/source/75ebf2c1033c64c1d81df13e4ae44ee99c989eba:ib_copy_udata.cocci
Link: http://marc.info/?i=cover.1394485254.git.ydroneaud@xxxxxxxxxx
Signed-off-by: Yann Droneaud <ydroneaud@xxxxxxxxxx>
Signed-off-by: Roland Dreier <roland@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/infiniband/hw/nes/nes_verbs.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/infiniband/hw/nes/nes_verbs.c
+++ b/drivers/infiniband/hw/nes/nes_verbs.c
@@ -1183,7 +1183,7 @@ static struct ib_qp *nes_create_qp(struc
 					nes_free_resource(nesadapter, nesadapter->allocated_qps, qp_num);
 					kfree(nesqp->allocated_buffer);
 					nes_debug(NES_DBG_QP, "ib_copy_from_udata() Failed \n");
-					return NULL;
+					return ERR_PTR(-EFAULT);
 				}
 				if (req.user_wqe_buffers) {
 					virt_wqs = 1;


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