| Message ID | 944215ec334c3c5b3af98210acf8f6479f5539c8.1445634103.git.calvinowens@fb.com (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
On 15-10-31 12:57 AM, Calvin Owens wrote: > 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> Thanks. > --- > 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 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; > + } > + > sg_finish_rem_req(srp); > return -ENODEV; > } > -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>>> "Doug" == Douglas Gilbert <dgilbert@interlog.com> writes: >> 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: >> Signed-off-by: Calvin Owens <calvinowens@fb.com> Doug> Acked-by: Douglas Gilbert <dgilbert@interlog.com> Applied.
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; + } + sg_finish_rem_req(srp); return -ENODEV; }
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> --- drivers/scsi/sg.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)