diff options
authorCalvin Owens <calvinowens@fb.com>2015-10-30 16:57:00 -0700
committerMartin K. Petersen <martin.petersen@oracle.com>2015-11-02 23:51:25 -0500
commitf3951a3709ff50990bf3e188c27d346792103432 (patch)
parentc913df3f3d6f7f5e5ed845e2786b0fc98a41482f (diff)
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: [<ffffffff81281eab>] blk_put_request+0x5b/0x80 [<ffffffffa0069e5b>] sg_finish_rem_req+0x6b/0x120 [sg] [<ffffffffa006bcb9>] sg_common_write.isra.14+0x459/0x5a0 [sg] [<ffffffff8125b328>] ? selinux_file_alloc_security+0x48/0x70 [<ffffffffa006bf95>] sg_new_write.isra.17+0x195/0x2d0 [sg] [<ffffffffa006cef4>] sg_ioctl+0x644/0xdb0 [sg] [<ffffffff81170f80>] do_vfs_ioctl+0x90/0x520 [<ffffffff81258967>] ? file_has_perm+0x97/0xb0 [<ffffffff811714a1>] SyS_ioctl+0x91/0xb0 [<ffffffff81602afb>] tracesys+0xdd/0xe2 RIP [<ffffffff81281e04>] __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 <calvinowens@fb.com> Acked-by: Douglas Gilbert <dgilbert@interlog.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
1 files changed, 7 insertions, 1 deletions
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 9d7b7db..503ab8b 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;
+ }
return -ENODEV;