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uml: fix request->sector update

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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>
This commit is contained in:
Jeff Dike 2007-07-15 23:38:47 -07:00 committed by Linus Torvalds
parent 7ff9057db7
commit 0a6d3a2a38
1 changed files with 4 additions and 2 deletions
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6
arch/um/drivers/ubd_kern.c
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@ -1083,7 +1083,7 @@ static void do_ubd_request(request_queue_t *q)
{
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 @@ static void do_ubd_request(request_queue_t *q)
}
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 @@ static void do_ubd_request(request_queue_t *q)
(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 @@ static void do_ubd_request(request_queue_t *q)
return;
}
req->sector += sg->length >> 9;
dev->start_sg++;
}
dev->end_sg = 0;