RDMA/siw: Fix a use after free in siw_alloc_mr

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: 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.

References

• https://git.kernel.org/stable/c/30b9e92d0b5e5d5dc1101ab856c17009537cbca4
• https://git.kernel.org/stable/c/608a4b90ece039940e9425ee2b39c8beff27e00c
• https://git.kernel.org/stable/c/3e22b88e02c194f6c80867abfef5cc09383461f4
• https://git.kernel.org/stable/c/ad9ce7188432650469a6c7625bf479f5ed0b6155
• https://git.kernel.org/stable/c/3093ee182f01689b89e9f8797b321603e5de4f63