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rds: ib: Clear the sg list when mapping an MR fails

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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: 1659185fb4 ("RDS: IB: Support Fastreg MR (FRMR) memory registration mode")
Cc: stable@vger.kernel.org
Signed-off-by: Dongliang Qin <cccccccccccc777777@gmail.com>
Reviewed-by: Allison Henderson <achender@kernel.org>
Link: https://patch.msgid.link/20260922031546.3874605-1-cccccccccccc777777@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Dongliang Qin 2026-09-22 11:15:45 +08:00 committed by Paolo Abeni
parent 77b1718e39
commit 58eb1b3325
1 changed files with 5 additions and 6 deletions
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11
net/rds/ib_frmr.c
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@ -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;
}