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 <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>

0 files changed, 0 insertions, 0 deletions