[PATCH] ipr: don't doublefree pages from scatterlist

[Hugh Dickins <hugh@veritas.com>]

On some architectures, mapping the scatterlist may coalesce entries:
if that coalesced list is then used for freeing the pages afterwards,
there's a danger that pages may be doubly freed (and others leaked).

Fix Power RAID's ipr_free_ucode_buffer by freeing from a separate array
beyond the scatterlist.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
---
Warning: untested!

 drivers/scsi/ipr.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

--- 2.6.16-rc2/drivers/scsi/ipr.c	2006-02-03 09:32:24.000000000 +0000
+++ linux/drivers/scsi/ipr.c	2006-02-03 09:59:37.000000000 +0000
@@ -2538,6 +2538,7 @@ static struct ipr_sglist *ipr_alloc_ucod
 	int sg_size, order, bsize_elem, num_elem, i, j;
 	struct ipr_sglist *sglist;
 	struct scatterlist *scatterlist;
+	struct page **sg_pages;
 	struct page *page;
 
 	/* Get the minimum size per scatter/gather element */
@@ -2557,7 +2558,8 @@ static struct ipr_sglist *ipr_alloc_ucod
 
 	/* Allocate a scatter/gather list for the DMA */
 	sglist = kzalloc(sizeof(struct ipr_sglist) +
-			 (sizeof(struct scatterlist) * (num_elem - 1)),
+			 (sizeof(struct scatterlist) * (num_elem - 1)) +
+			 (sizeof(struct page *) * num_elem),
 			 GFP_KERNEL);
 
 	if (sglist == NULL) {
@@ -2566,6 +2568,8 @@ static struct ipr_sglist *ipr_alloc_ucod
 	}
 
 	scatterlist = sglist->scatterlist;
+	/* Save pages to be freed in array beyond scatterlist */
+	sg_pages = (struct page **) (scatterlist + num_elem);
 
 	sglist->order = order;
 	sglist->num_sg = num_elem;
@@ -2584,6 +2588,7 @@ static struct ipr_sglist *ipr_alloc_ucod
 		}
 
 		scatterlist[i].page = page;
+		sg_pages[i] = page;
 	}
 
 	return sglist;
@@ -2601,10 +2606,13 @@ static struct ipr_sglist *ipr_alloc_ucod
  **/
 static void ipr_free_ucode_buffer(struct ipr_sglist *sglist)
 {
+	struct page **sg_pages;
 	int i;
 
+	/* Scatterlist entries may have been coalesced: free saved pagelist */
+	sg_pages = (struct page **) (sglist->scatterlist + sglist->num_sg);
 	for (i = 0; i < sglist->num_sg; i++)
-		__free_pages(sglist->scatterlist[i].page, sglist->order);
+		__free_pages(sg_pages[i], sglist->order);
 
 	kfree(sglist);
 }
-
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