linux-kernel - [PATCH 4.19 028/100] zram: pass down the bvec we need to read into in the work struct

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Date:   Tue, 30 Apr 2019 13:37:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Minchan Kim <minchan@...nel.org>,
        Nitin Gupta <ngupta@...are.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.19 028/100] zram: pass down the bvec we need to read into in the work struct

From: Jérôme Glisse <jglisse@...hat.com>

commit e153abc0739ff77bd89c9ba1688cdb963464af97 upstream.

When scheduling work item to read page we need to pass down the proper
bvec struct which points to the page to read into.  Before this patch it
uses a randomly initialized bvec (only if PAGE_SIZE != 4096) which is
wrong.

Note that without this patch on arch/kernel where PAGE_SIZE != 4096
userspace could read random memory through a zram block device (thought
userspace probably would have no control on the address being read).

Link: http://lkml.kernel.org/r/20190408183219.26377-1-jglisse@redhat.com
Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
Reviewed-by: Andrew Morton <akpm@...ux-foundation.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Acked-by: Minchan Kim <minchan@...nel.org>
Cc: Nitin Gupta <ngupta@...are.org>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/block/zram/zram_drv.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -515,18 +515,18 @@ struct zram_work {
 	struct zram *zram;
 	unsigned long entry;
 	struct bio *bio;
+	struct bio_vec bvec;
 };
 
 #if PAGE_SIZE != 4096
 static void zram_sync_read(struct work_struct *work)
 {
-	struct bio_vec bvec;
 	struct zram_work *zw = container_of(work, struct zram_work, work);
 	struct zram *zram = zw->zram;
 	unsigned long entry = zw->entry;
 	struct bio *bio = zw->bio;
 
-	read_from_bdev_async(zram, &bvec, entry, bio);
+	read_from_bdev_async(zram, &zw->bvec, entry, bio);
 }
 
 /*
@@ -539,6 +539,7 @@ static int read_from_bdev_sync(struct zr
 {
 	struct zram_work work;
 
+	work.bvec = *bvec;
 	work.zram = zram;
 	work.entry = entry;
 	work.bio = bio;