| Message ID | 1497013013-82129-2-git-send-email-brad.figg@canonical.com |
|---|---|
| State | New |
| Headers | show |
On 09/06/17 13:56, Brad Figg wrote: > From: Calvin Owens <calvinowens@fb.com> > > CVE-2015-8962 > > 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> > (backported from commit f3951a3709ff50990bf3e188c27d346792103432 upstream) > Signed-off-by: Brad Figg <brad.figg@canonical.com> > --- > drivers/scsi/sg.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c > index 1f65e32..0d512d4 100644 > --- a/drivers/scsi/sg.c > +++ b/drivers/scsi/sg.c > @@ -766,8 +766,13 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp, > return k; /* probably out of space --> ENOMEM */ > } > if (sdp->detached) { > - if (srp->bio) > - blk_end_request_all(srp->rq, -EIO); > + 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; > } > I believe this backport is good, had to double check this against the original fix. Acked-by: Colin Ian King <colin.king@canonical.com>
On Fri, Jun 09, 2017 at 05:56:53AM -0700, Brad Figg wrote: > From: Calvin Owens <calvinowens@fb.com> > > CVE-2015-8962 > > 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> > (backported from commit f3951a3709ff50990bf3e188c27d346792103432 upstream) > Signed-off-by: Brad Figg <brad.figg@canonical.com> > --- > drivers/scsi/sg.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c > index 1f65e32..0d512d4 100644 > --- a/drivers/scsi/sg.c > +++ b/drivers/scsi/sg.c > @@ -766,8 +766,13 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp, > return k; /* probably out of space --> ENOMEM */ > } > if (sdp->detached) { > - if (srp->bio) > - blk_end_request_all(srp->rq, -EIO); > + 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; > } This seems to do what is hoped. I think this one needs a bit of testing to be 100% confident. But: Acked-by: Andy Whitcroft <apw@canonical.com> -apw
Applied to Trusty master-next (fixing up one whitespace error). Thanks, -Stefan
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index 1f65e32..0d512d4 100644 --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -766,8 +766,13 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp, return k; /* probably out of space --> ENOMEM */ } if (sdp->detached) { - if (srp->bio) - blk_end_request_all(srp->rq, -EIO); + 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; }