[PATCH rdma-next 05/10] RDMA/core: Fix potential use after free in ib_destroy_srq_user()

[Edward Srouji <edwards@nvidia.com>]

From: Patrisious Haddad <phaddad@nvidia.com>

When accessing a SRQ via the netlink path the only synchronization
mechanism for the said SRQ is rdma_restrack_get().
Currently, rdma_restrack_del() is invoked at the end of
ib_destroy_srq_user(), which is too late, since by that point
vendor-specific resources associated with the SRQ might already be
freed. This can leave a short window where the SRQ remains accessible
through restrack, leading to a potential use-after-free.

Fix this by moving the rdma_restrack_del() call to the start of
ib_destroy_srq_user(), ensuring that the SRQ is removed from restrack
before its internal resources are released. This guarantees that no new
users hold references to a SRQ that is in the process of destruction.

In addition, this change preserves the intended asymmetric behavior
between create and destroy routines: resources are added to
restrack at the end of successful creation, and hence shall be removed
from the restrack first thing during the destruction flow, which keeps
the lifecycle management consistent and predictable.

Fixes: 48f8a70e899f ("RDMA/restrack: Add support to get resource tracking for SRQ")
Signed-off-by: Patrisious Haddad <phaddad@nvidia.com>
Reviewed-by: Michael Guralnik <michaelgur@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
---
 drivers/infiniband/core/verbs.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/verbs.c b/drivers/infiniband/core/verbs.c
index 0e8f99807c7c0ce063ed0c1561f4ba42b485b69d..5921c6d008bb10bcce5f3b9bcc99de72193941db 100644
--- a/drivers/infiniband/core/verbs.c
+++ b/drivers/infiniband/core/verbs.c
@@ -1139,16 +1139,20 @@ int ib_destroy_srq_user(struct ib_srq *srq, struct ib_udata *udata)
 	if (atomic_read(&srq->usecnt))
 		return -EBUSY;
 
+	rdma_restrack_del(&srq->res);
+
 	ret = srq->device->ops.destroy_srq(srq, udata);
-	if (ret)
+	if (ret) {
+		rdma_restrack_new(&srq->res, RDMA_RESTRACK_SRQ);
+		rdma_restrack_add(&srq->res);
 		return ret;
+	}
 
 	atomic_dec(&srq->pd->usecnt);
 	if (srq->srq_type == IB_SRQT_XRC && srq->ext.xrc.xrcd)
 		atomic_dec(&srq->ext.xrc.xrcd->usecnt);
 	if (ib_srq_has_cq(srq->srq_type))
 		atomic_dec(&srq->ext.cq->usecnt);
-	rdma_restrack_del(&srq->res);
 	kfree(srq);
 
 	return ret;

-- 
2.49.0