Re: [PATCH v2] rdma/siw: Fix a use after free in siw_alloc_mr

[Bernard Metzler]

-----"Lv Yunlong" <lyl2019@xxxxxxxxxxxxxxxx> wrote: -----

>To: bmt@xxxxxxxxxxxxxx, dledford@xxxxxxxxxx, jgg@xxxxxxxx
>From: "Lv Yunlong" <lyl2019@xxxxxxxxxxxxxxxx>
>Date: 04/26/2021 03:17AM
>Cc: linux-rdma@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, "Lv
>Yunlong" <lyl2019@xxxxxxxxxxxxxxxx>
>Subject: [EXTERNAL] [PATCH v2] rdma/siw: Fix a use after free in
>siw_alloc_mr
>
>Our code analyzer reported a uaf.
>
>In siw_alloc_mr, it calls siw_mr_add_mem(mr,..). In the
>implementation
>of siw_mr_add_mem(), mem is assigned to mr->mem and then mem is freed
>via kfree(mem) if xa_alloc_cyclic() failed. Here, mr->mem still point
>to a freed object. After, the execution continue up to the err_out
>branch
>of siw_alloc_mr, and the freed mr->mem is used in
>siw_mr_drop_mem(mr).
>
>My patch moves "mr->mem = mem" behind the if (xa_alloc_cyclic(..)<0)
>{}
>section, to avoid the uaf.
>
>Fixes: 2251334dcac9e ("rdma/siw: application buffer management")
>Signed-off-by: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>
>---
> drivers/infiniband/sw/siw/siw_mem.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/infiniband/sw/siw/siw_mem.c
>b/drivers/infiniband/sw/siw/siw_mem.c
>index 34a910cf0edb..96b38cfbb513 100644
>--- a/drivers/infiniband/sw/siw/siw_mem.c
>+++ b/drivers/infiniband/sw/siw/siw_mem.c
>@@ -106,8 +106,6 @@ int siw_mr_add_mem(struct siw_mr *mr, struct
>ib_pd *pd, void *mem_obj,
> 	mem->perms = rights & IWARP_ACCESS_MASK;
> 	kref_init(&mem->ref);
> 
>-	mr->mem = mem;
>-
> 	get_random_bytes(&next, 4);
> 	next &= 0x00ffffff;
> 
>@@ -116,6 +114,8 @@ int siw_mr_add_mem(struct siw_mr *mr, struct
>ib_pd *pd, void *mem_obj,
> 		kfree(mem);
> 		return -ENOMEM;
> 	}
>+
>+	mr->mem = mem;
> 	/* Set the STag index part */
> 	mem->stag = id << 8;
> 	mr->base_mr.lkey = mr->base_mr.rkey = mem->stag;
>-- 
>2.25.1
>
>
>
Lv Yunlong, many thanks for catching, and thanks to
Leon for improving it.

Reviewed-by: Bernard Metzler <bmt@xxxxxxxxxxxxxx>