zram: pass down the bvec we need to read into in the work struct [Linux 5.1]

zram: pass down the bvec we need to read into in the work struct [Linux 5.1]

This Linux kernel change "zram: pass down the bvec we need to read into in the work struct" is included in the Linux 5.1 release. This change is authored by Jérôme Glisse <jglisse [at] redhat.com> on Thu Apr 25 22:23:41 2019 -0700. The commit for this change in Linux stable tree is e153abc (patch).

zram: pass down the bvec we need to read into in the work struct

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@redhat.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

There are 5 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

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

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 399cad7..d58a359 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -774,18 +774,18 @@ 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);
 }

 /*
@@ -798,6 +798,7 @@ static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
 {
    struct zram_work work;

+   work.bvec = *bvec;
    work.zram = zram;
    work.entry = entry;
    work.bio = bio;

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