Re: [PATCH] md-cluster: Fix potential error pointer dereference in resize_bitmaps()

On Tue, Aug 4, 2020 at 4:16 AM Dan Carpenter [off-list ref] wrote:

On Tue, Aug 04, 2020 at 12:40:18PM +0200, Guoqing Jiang wrote:

quoted

On 8/4/20 12:16 PM, Dan Carpenter wrote:

quoted

The error handling calls md_bitmap_free(bitmap) which checks for NULL
but will Oops if we pass an error pointer.  Let's set "bitmap" to NULL
on this error path.

Fixes: afd756286083 ("md-cluster/raid10: resize all the bitmaps before start reshape")
Signed-off-by: Dan Carpenter <redacted>
---
  drivers/md/md-cluster.c | 1 +
  1 file changed, 1 insertion(+)

diff --git a/drivers/md/md-cluster.c b/drivers/md/md-cluster.c
index 73fd50e77975..d50737ec4039 100644
--- a/drivers/md/md-cluster.c
+++ b/drivers/md/md-cluster.c

@@ -1139,6 +1139,7 @@ static int resize_bitmaps(struct mddev *mddev, sector_t newsize, sector_t oldsiz
            bitmap = get_bitmap_from_slot(mddev, i);
            if (IS_ERR(bitmap)) {
                    pr_err("can't get bitmap from slot %d\n", i);
+                   bitmap = NULL;
                    goto out;
            }
            counts = &bitmap->counts;

Thanks for the catch, Reviewed-by: Guoqing Jiang
[off-list ref]

BTW, seems there could be memory leak in the function since it keeps
allocate bitmap
in the loop ..., will send a format patch.

diff --git a/drivers/md/md-cluster.c b/drivers/md/md-cluster.c
index 73fd50e77975..89d7b32489d8 100644
--- a/drivers/md/md-cluster.c
+++ b/drivers/md/md-cluster.c

@@ -1165,6 +1165,8 @@ static int resize_bitmaps(struct mddev *mddev,

sector_t newsize, sector_t oldsiz
                         * can't resize bitmap
                         */
                        goto out;
+
+               md_bitmap_free(bitmap);

Hm...  I'm now not at all certain my patch is correct.  Although it's
obviously harmless and fixes an Oops.  I had thought that that the call
to update_bitmap_size(mddev, oldsize) would free the rest of the loop.

I really suspect adding a free like you're suggesting will break the
success path.

I'm not familiar with this code at all.

Thanks Dan and Guoqing. I applied Dans' patch to md-next.

I think we are leaking bitmap in resize_bitmaps(). But we gonna need
more complex fix than the md_bitmap_free() above.

Thanks,
Song