scsi: bsg: copy uring_cmd payload to prevent double-fetch from shared SQE#895
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… SQE scsi_bsg_uring_cmd() and scsi_bsg_map_user_buffer() read bsg_uring_cmd fields directly from the shared mmap'd io_uring submission ring via io_uring_sqe128_cmd(). On the inline execution path, io_uring has not yet copied the SQE to kernel memory, so a concurrent userspace thread can modify fields between reads. cmd->request_len is read for the bounds check, for the cmd_len assignment, and for the copy_from_user length. A racing thread can change request_len between the bounds check (passes with <= 32) and copy_from_user (uses the enlarged value), overflowing the 32-byte scmd->cmnd[] buffer into subsequent struct scsi_cmnd fields. scsi_bsg_map_user_buffer() independently re-derives its cmd pointer from the same shared SQE, re-reading dout_xfer_len, din_xfer_len, dout_xferp, and din_xferp, enabling direction confusion and buffer length races. Copy struct bsg_uring_cmd to a stack-local variable before use in both functions. The pointer variable 'cmd' is redirected to the local copy so the rest of each function is unchanged. Tested with KASAN on QEMU (virtio-scsi, 2 vCPUs). Without this fix, a two-thread race produces: BUG: KASAN: wild-memory-access in scsi_queue_rq+0x4a3/0x58a0 Write of size 96 at addr dead000000001000 by task poc/67 Call Trace: kasan_report+0xce/0x100 __asan_memset+0x23/0x50 scsi_queue_rq+0x4a3/0x58a0 scsi_bsg_uring_cmd+0x942/0x1570 io_uring_cmd+0x2f6/0x950 io_issue_sqe+0xe5/0x22d0 Fixes: 7b6d325 ("scsi: bsg: add io_uring passthrough handler") Cc: stable@vger.kernel.org Signed-off-by: Rahul Chandelkar <rc@rexion.ai> Reviewed-by: Bart Van Assche <bvanassche@acm.org>
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Pull request for series with
subject: scsi: bsg: copy uring_cmd payload to prevent double-fetch from shared SQE
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1101589