From f3951a3709ff50990bf3e188c27d346792103432 Mon Sep 17 00:00:00 2001 From: Calvin Owens Date: Fri, 30 Oct 2015 16:57:00 -0700 Subject: [PATCH] sg: Fix double-free when drives detach during SG_IO In sg_common_write(), we free the block request and return -ENODEV if the device is detached in the middle of the SG_IO ioctl(). Unfortunately, sg_finish_rem_req() also tries to free srp->rq, so we end up freeing rq->cmd in the already free rq object, and then free the object itself out from under the current user. This ends up corrupting random memory via the list_head on the rq object. The most common crash trace I saw is this: ------------[ cut here ]------------ kernel BUG at block/blk-core.c:1420! Call Trace: [] blk_put_request+0x5b/0x80 [] sg_finish_rem_req+0x6b/0x120 [sg] [] sg_common_write.isra.14+0x459/0x5a0 [sg] [] ? selinux_file_alloc_security+0x48/0x70 [] sg_new_write.isra.17+0x195/0x2d0 [sg] [] sg_ioctl+0x644/0xdb0 [sg] [] do_vfs_ioctl+0x90/0x520 [] ? file_has_perm+0x97/0xb0 [] SyS_ioctl+0x91/0xb0 [] tracesys+0xdd/0xe2 RIP [] __blk_put_request+0x154/0x1a0 The solution is straightforward: just set srp->rq to NULL in the failure branch so that sg_finish_rem_req() doesn't attempt to re-free it. Additionally, since sg_rq_end_io() will never be called on the object when this happens, we need to free memory backing ->cmd if it isn't embedded in the object itself. KASAN was extremely helpful in finding the root cause of this bug. Signed-off-by: Calvin Owens Acked-by: Douglas Gilbert Signed-off-by: Martin K. Petersen --- drivers/scsi/sg.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index 9d7b7db75e4b..503ab8b46c0b 100644 --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -787,8 +787,14 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp, return k; /* probably out of space --> ENOMEM */ } if (atomic_read(&sdp->detaching)) { - if (srp->bio) + if (srp->bio) { + if (srp->rq->cmd != srp->rq->__cmd) + kfree(srp->rq->cmd); + blk_end_request_all(srp->rq, -EIO); + srp->rq = NULL; + } + sg_finish_rem_req(srp); return -ENODEV; } -- 2.20.1