Messages in this thread Patch in this message | | | From | Konrad Rzeszutek Wilk <> | Subject | [PATCH 2/2] xen/blkfront: Add BUG_ON to deal with misbehaving backends. | Date | Fri, 25 May 2012 17:50:03 -0400 |
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Part of the ring structure is the 'id' field which is under control of the frontend. The frontend stamps it with "some" value (this some in this implementation being a value less than BLK_RING_SIZE), and when it gets a response expects said value to be in the response structure. We have a check for the id field when spolling new requests but not when de-spolling responses.
We also add an extra check in add_id_to_freelist to make sure that the 'struct request' was not NULL - as we cannot pass a NULL to __blk_end_request_all, otherwise that crashes (and all the operations that the response is dealing with end up with __blk_end_request_all).
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> --- drivers/block/xen-blkfront.c | 7 +++++++ 1 files changed, 7 insertions(+), 0 deletions(-)
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index 60eed4b..8e177ca 100644 --- a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c @@ -145,6 +145,7 @@ static void add_id_to_freelist(struct blkfront_info *info, unsigned long id) { info->shadow[id].req.u.rw.id = info->shadow_free; + BUG_ON(info->shadow[id].request == NULL); info->shadow[id].request = NULL; info->shadow_free = id; } @@ -746,6 +747,12 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id) bret = RING_GET_RESPONSE(&info->ring, i); id = bret->id; + /* + * The backend has messed up and given us an id that we would + * never have given to it (we stamp it up to BLK_RING_SIZE - + * look in get_id_from_freelist. + */ + BUG_ON(id >= BLK_RING_SIZE); req = info->shadow[id].request; if (bret->operation != BLKIF_OP_DISCARD) -- 1.7.7.6
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