[PATCH rdma-next 8/8] RDMA/core: Fix potential use after free in ib_dealloc_pd_user()

[Edward Srouji <edwards@nvidia.com>]

From: Patrisious Haddad <phaddad@nvidia.com>

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

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

In addition, this change preserves the intended inverted order
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: 91a7c58fce06 ("RDMA: Restore ability to fail on PD deallocate")
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 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/verbs.c b/drivers/infiniband/core/verbs.c
index bfbc25dee95d031f91ffef5389e81faa08170719..f86e6f30b1df08396c151000fa7184574a034e0f 100644
--- a/drivers/infiniband/core/verbs.c
+++ b/drivers/infiniband/core/verbs.c
@@ -392,6 +392,7 @@ int ib_dealloc_pd_user(struct ib_pd *pd, struct ib_udata *udata)
 {
 	int ret;
 
+	rdma_restrack_begin_del(&pd->res);
 	if (pd->__internal_mr) {
 		ret = pd->device->ops.dereg_mr(pd->__internal_mr, NULL);
 		WARN_ON(ret);
@@ -399,10 +400,12 @@ int ib_dealloc_pd_user(struct ib_pd *pd, struct ib_udata *udata)
 	}
 
 	ret = pd->device->ops.dealloc_pd(pd, udata);
-	if (ret)
+	if (ret) {
+		rdma_restrack_abort_del(&pd->res);
 		return ret;
+	}
 
-	rdma_restrack_del(&pd->res);
+	rdma_restrack_commit_del(&pd->res);
 	kfree(pd);
 	return ret;
 }

-- 
2.49.0