lkml.org 
[lkml]   [2007]   [Jun]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH 1/2] UML - Fix request->sector update
[ This is post-2.6.22 material - it fixes a bug, but not one that I
think has been seen in the wild, plus an earlier version of this fix
caused file corruption ]

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>
--
arch/um/drivers/ubd_kern.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

Index: linux-2.6.21-mm/arch/um/drivers/ubd_kern.c
===================================================================
--- linux-2.6.21-mm.orig/arch/um/drivers/ubd_kern.c 2007-06-02 12:13:50.000000000 -0400
+++ linux-2.6.21-mm/arch/um/drivers/ubd_kern.c 2007-06-02 22:23:41.000000000 -0400
@@ -1082,7 +1082,7 @@ static void do_ubd_request(request_queue
{
struct io_thread_req *io_req;
struct request *req;
- int n;
+ int n, last_sectors;

while(1){
struct ubd *dev = q->queuedata;
@@ -1098,9 +1098,11 @@ static void do_ubd_request(request_queue
}

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){
@@ -1112,6 +1114,7 @@ static void do_ubd_request(request_queue
(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 *)){
@@ -1123,7 +1126,6 @@ static void do_ubd_request(request_queue
return;
}

- req->sector += sg->length >> 9;
dev->start_sg++;
}
dev->end_sg = 0;
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2007-06-05 23:01    [W:0.181 / U:0.092 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site