uml: fix request->sector update
It is theoretically possible for a request to finish and be freed between
writing it to the I/O thread and updating the sector count. In this case, the
update will dereference a freed pointer.
To avoid this, I delay the update until processing the next sg segment, when
the request pointer is known to be good.
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 2e09f16..0947f2e 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -1083,7 +1083,7 @@
{
struct io_thread_req *io_req;
struct request *req;
- int n;
+ int n, last_sectors;
while(1){
struct ubd *dev = q->queuedata;
@@ -1099,9 +1099,11 @@
}
req = dev->request;
+ last_sectors = 0;
while(dev->start_sg < dev->end_sg){
struct scatterlist *sg = &dev->sg[dev->start_sg];
+ req->sector += last_sectors;
io_req = kmalloc(sizeof(struct io_thread_req),
GFP_ATOMIC);
if(io_req == NULL){
@@ -1113,6 +1115,7 @@
(unsigned long long) req->sector << 9,
sg->offset, sg->length, sg->page);
+ last_sectors = sg->length >> 9;
n = os_write_file(thread_fd, &io_req,
sizeof(struct io_thread_req *));
if(n != sizeof(struct io_thread_req *)){
@@ -1124,7 +1127,6 @@
return;
}
- req->sector += sg->length >> 9;
dev->start_sg++;
}
dev->end_sg = 0;