RDMA/cxgb4: Add missing padding at end of struct c4iw_create_cq_resp
The i386 ABI disagrees with most other ABIs regarding alignment of
data types larger than 4 bytes: on most ABIs a padding must be added
at end of the structures, while it is not required on i386.
So for most ABI struct c4iw_create_cq_resp gets implicitly padded
to be aligned on a 8 bytes multiple, while for i386, such padding
is not added.
The tool pahole can be used to find such implicit padding:
$ pahole --anon_include \
--nested_anon_include \
--recursive \
--class_name c4iw_create_cq_resp \
drivers/infiniband/hw/cxgb4/iw_cxgb4.o
Then, structure layout can be compared between i386 and x86_64:
+++ obj-i386/drivers/infiniband/hw/cxgb4/iw_cxgb4.o.pahole.txt 2014-03-28 11:43:05.547432195 +0100
--- obj-x86_64/drivers/infiniband/hw/cxgb4/iw_cxgb4.o.pahole.txt 2014-03-28 10:55:10.990133017 +0100
@@ -14,9 +13,8 @@ struct c4iw_create_cq_resp {
__u32 size; /* 28 4 */
__u32 qid_mask; /* 32 4 */
- /* size: 36, cachelines: 1, members: 6 */
- /* last cacheline: 36 bytes */
+ /* size: 40, cachelines: 1, members: 6 */
+ /* padding: 4 */
+ /* last cacheline: 40 bytes */
};
This ABI disagreement will make an x86_64 kernel try to write past the
buffer provided by an i386 binary.
When boundary check will be implemented, the x86_64 kernel will refuse
to write past the i386 userspace provided buffer and the uverbs will
fail.
If the structure is on a page boundary and the next page is not
mapped, ib_copy_to_udata() will fail and the uverb will fail.
This patch adds an explicit padding at end of structure
c4iw_create_cq_resp, and, like 92b0ca7cb149 ("IB/mlx5: Fix stack info
leak in mlx5_ib_alloc_ucontext()"), makes function c4iw_create_cq()
not writting this padding field to userspace. This way, x86_64 kernel
will be able to write struct c4iw_create_cq_resp as expected by
unpatched and patched i386 libcxgb4.
Link: http://marc.info/?i=cover.1399309513.git.ydroneaud@opteya.com
Cc: <stable@vger.kernel.org>
Fixes: cfdda9d764362 ("RDMA/cxgb4: Add driver for Chelsio T4 RNIC")
Fixes: e24a72a3302a6 ("RDMA/cxgb4: Fix four byte info leak in c4iw_create_cq()")
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
2 files changed