4.4-stable review patch. If anyone has any objections, please let me know.
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From: Lars Ellenberg lars.ellenberg@linbit.com
commit 64dafbc9530c10300acffc57fae3269d95fa8f93 upstream.
We have struct drbd_requests { ... struct bio *private_bio; ... } to hold a bio clone for local submission.
On local IO completion, we put that bio, and in case we want to use the result later, we overload that member to hold the ERR_PTR() of the completion result,
Which, before v4.3, used to be the passed in "int error", so we could first bio_put(), then assign.
v4.3-rc1~100^2~21 4246a0b63bd8 block: add a bi_error field to struct bio changed that: bio_put(req->private_bio); - req->private_bio = ERR_PTR(error); + req->private_bio = ERR_PTR(bio->bi_error);
Which introduces an access after free, because it was non obvious that req->private_bio == bio.
Impact of that was mostly unnoticable, because we only use that value in a multiple-failure case, and even then map any "unexpected" error code to EIO, so worst case we could potentially mask a more specific error with EIO in a multiple failure case.
Unless the pointed to memory region was unmapped, as is the case with CONFIG_DEBUG_PAGEALLOC, in which case this results in
BUG: unable to handle kernel paging request
v4.13-rc1~70^2~75 4e4cbee93d56 block: switch bios to blk_status_t changes it further to bio_put(req->private_bio); req->private_bio = ERR_PTR(blk_status_to_errno(bio->bi_status));
And blk_status_to_errno() now contains a WARN_ON_ONCE() for unexpected values, which catches this "sometimes", if the memory has been reused quickly enough for other things.
Should also go into stable since 4.3, with the trivial change around 4.13.
Cc: stable@vger.kernel.org Fixes: 4246a0b63bd8 block: add a bi_error field to struct bio Reported-by: Sarah Newman srn@prgmr.com Signed-off-by: Lars Ellenberg lars.ellenberg@linbit.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/block/drbd/drbd_worker.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/block/drbd/drbd_worker.c +++ b/drivers/block/drbd/drbd_worker.c @@ -256,8 +256,8 @@ void drbd_request_endio(struct bio *bio) } else what = COMPLETED_OK;
- bio_put(req->private_bio); req->private_bio = ERR_PTR(bio->bi_error); + bio_put(bio);
/* not req_mod(), we need irqsave here! */ spin_lock_irqsave(&device->resource->req_lock, flags);