[PATCH v2] RDMA/rxe: Fix double free in rxe_srq_from_init

[Jiasheng Jiang <jiashengjiangcool@gmail.com>]

In rxe_srq_from_init(), the queue pointer 'q' is assigned to
'srq->rq.queue' before copying the SRQ number to user space.
If copy_to_user() fails, the function calls rxe_queue_cleanup()
to free the queue, but leaves the now-invalid pointer in
'srq->rq.queue'.

The caller of rxe_srq_from_init() (rxe_create_srq) eventually
calls rxe_srq_cleanup() upon receiving the error, which triggers
a second rxe_queue_cleanup() on the same memory, leading to a
double free.

The call trace looks like this:
   kmem_cache_free+0x.../0x...
   rxe_queue_cleanup+0x1a/0x30 [rdma_rxe]
   rxe_srq_cleanup+0x42/0x60 [rdma_rxe]
   rxe_elem_release+0x31/0x70 [rdma_rxe]
   rxe_create_srq+0x12b/0x1a0 [rdma_rxe]
   ib_create_srq_user+0x9a/0x150 [ib_core]

Fix this by moving 'srq->rq.queue = q' after copy_to_user.

Fixes: aae0484e15f0 ("IB/rxe: avoid srq memory leak")
Signed-off-by: Jiasheng Jiang <jiashengjiangcool@gmail.com>
---
Changelog:

v1 -> v2:

1. Move both 'srq->rq.queue = q' and 'init->attr.max_wr = srq->rq.max_wr'
after copy_to_user().
2. Add call trace for better understanding of the issue.
---
 drivers/infiniband/sw/rxe/rxe_srq.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_srq.c b/drivers/infiniband/sw/rxe/rxe_srq.c
index 2a234f26ac10..c9a7cd38953d 100644
--- a/drivers/infiniband/sw/rxe/rxe_srq.c
+++ b/drivers/infiniband/sw/rxe/rxe_srq.c
@@ -77,9 +77,6 @@ int rxe_srq_from_init(struct rxe_dev *rxe, struct rxe_srq *srq,
 		goto err_free;
 	}
 
-	srq->rq.queue = q;
-	init->attr.max_wr = srq->rq.max_wr;
-
 	if (uresp) {
 		if (copy_to_user(&uresp->srq_num, &srq->srq_num,
 				 sizeof(uresp->srq_num))) {
@@ -88,6 +85,9 @@ int rxe_srq_from_init(struct rxe_dev *rxe, struct rxe_srq *srq,
 		}
 	}
 
+	srq->rq.queue = q;
+	init->attr.max_wr = srq->rq.max_wr;
+
 	return 0;
 
 err_free:
-- 
2.25.1