When IORING_REGISTER_CLONE_BUFFERS is used to clone buffers from uring instance A to uring instance B, where A and B use different MMs for accounting, the accounting can go wrong: If uring instance A is closed before uring instance B, the pinned memory counters for uring instance B will be decremented, even though the pinned memory was originally accounted through uring instance A; so the MM of uring instance B can end up with negative locked memory. Cc: stable@xxxxxxxxxxxxxxx Closes: https://lore.kernel.org/r/CAG48ez1zez4bdhmeGLEFxtbFADY4Czn3CV0u9d_TMcbvRA01bg@xxxxxxxxxxxxxx Fixes: 7cc2a6eadcd7 ("io_uring: add IORING_REGISTER_COPY_BUFFERS method") Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> Link: https://lore.kernel.org/r/20250114-uring-check-accounting-v1-1-42e4145aa743@xxxxxxxxxx Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c index 964a47c8d85e..688e277f0335 100644 --- a/io_uring/rsrc.c +++ b/io_uring/rsrc.c @@ -928,6 +928,13 @@ static int io_clone_buffers(struct io_ring_ctx *ctx, struct io_ring_ctx *src_ctx int i, ret, off, nr; unsigned int nbufs; + /* + * Accounting state is shared between the two rings; that only works if + * both rings are accounted towards the same counters. + */ + if (ctx->user != src_ctx->user || ctx->mm_account != src_ctx->mm_account) + return -EINVAL; + /* if offsets are given, must have nr specified too */ if (!arg->nr && (arg->dst_off || arg->src_off)) return -EINVAL;
