3.2.85-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Calvin Owens <calvinowens@xxxxxx>
commit f3951a3709ff50990bf3e188c27d346792103432 upstream.
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@xxxxxx>
Acked-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
[bwh: Backported to 3.2:
- sg_finish_rem_req() would not free srp->rq->cmd so don't do it here either
- Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
drivers/scsi/sg.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -742,8 +742,11 @@ sg_common_write(Sg_fd * sfp, Sg_request
return k; /* probably out of space --> ENOMEM */
}
if (sdp->detached) {
- if (srp->bio)
+ if (srp->bio) {
blk_end_request_all(srp->rq, -EIO);
+ srp->rq = NULL;
+ }
+
sg_finish_rem_req(srp);
return -ENODEV;
}