From 58eb1b3325edac42dc6df72c80962bd53a3c8ca7 Mon Sep 17 00:00:00 2001 From: Dongliang Qin Date: Tue, 22 Sep 2026 11:15:45 +0800 Subject: [PATCH] rds: ib: Clear the sg list when mapping an MR fails rds_ib_map_frmr() stores the caller's scatterlist in the MR before DMA mapping and registration can fail. On failure, __rds_rdma_map() unpins the pages and frees the scatterlist, but rds_ib_free_frmr() can still return the MR to the pool with the stale pointer set. This leaves the pool with a dangling scatterlist and can lead to local privilege escalation. KASAN detects the resulting use-after-free when the MR is later torn down: BUG: KASAN: slab-use-after-free in __rds_ib_teardown_mr Read of size 8 Call Trace: __rds_ib_teardown_mr rds_ib_unreg_frmr rds_ib_flush_mr_pool rds_ib_flush_mrs rds_free_mr rds_setsockopt Store the scatterlist in the MR only after DMA mapping succeeds. If DMA mapping fails, return directly while the MR fields remain clear; the caller keeps ownership of the scatterlist and its pinned pages. If a later registration step fails, unmap the scatterlist and clear the MR fields before returning. Fixes: 1659185fb4d0 ("RDS: IB: Support Fastreg MR (FRMR) memory registration mode") Cc: stable@vger.kernel.org Signed-off-by: Dongliang Qin Reviewed-by: Allison Henderson Link: https://patch.msgid.link/20260922031546.3874605-1-cccccccccccc777777@gmail.com Signed-off-by: Paolo Abeni --- net/rds/ib_frmr.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/net/rds/ib_frmr.c b/net/rds/ib_frmr.c index bd861191157b..8397aa4a17ac 100644 --- a/net/rds/ib_frmr.c +++ b/net/rds/ib_frmr.c @@ -204,19 +204,16 @@ static int rds_ib_map_frmr(struct rds_ib_device *rds_ibdev, */ rds_ib_teardown_mr(ibmr); - ibmr->sg = sg; - ibmr->sg_len = sg_len; - ibmr->sg_dma_len = 0; frmr->sg_byte_len = 0; - WARN_ON(ibmr->sg_dma_len); - ibmr->sg_dma_len = ib_dma_map_sg(dev, ibmr->sg, ibmr->sg_len, + ibmr->sg_dma_len = ib_dma_map_sg(dev, sg, sg_len, DMA_BIDIRECTIONAL); if (unlikely(!ibmr->sg_dma_len)) { pr_warn("RDS/IB: %s failed!\n", __func__); return -EBUSY; } - frmr->sg_byte_len = 0; + ibmr->sg = sg; + ibmr->sg_len = sg_len; frmr->dma_npages = 0; len = 0; @@ -264,6 +261,8 @@ static int rds_ib_map_frmr(struct rds_ib_device *rds_ibdev, ib_dma_unmap_sg(rds_ibdev->dev, ibmr->sg, ibmr->sg_len, DMA_BIDIRECTIONAL); ibmr->sg_dma_len = 0; + ibmr->sg = NULL; + ibmr->sg_len = 0; return ret; }