[PATCH] misc: genwqe: check for error from get_user_pages_fast()

[Ian Abbott]

`genwqe_user_vmap()` calls `get_user_pages_fast()` and if the return
value is less than the number of pages requested, it frees the pages and
returns an error (`-EFAULT`).  However, it fails to consider a negative
error return value from `get_user_pages_fast()`.  In that case, the test
`if (rc < m->nr_pages)` will be false (due to promotion of `rc` to a
large `unsigned int`) and the code will continue on to call
`genwqe_map_pages()` with an invalid list of page pointers.  Fix it by
bailing out if `get_user_pages_fast()` returns a negative error value.

Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 3.14.x # 3.15.x # 3.16.x # 3.17.x
---
 drivers/misc/genwqe/card_utils.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/misc/genwqe/card_utils.c b/drivers/misc/genwqe/card_utils.c
index 7cb3b7e..1ca94e6 100644
--- a/drivers/misc/genwqe/card_utils.c
+++ b/drivers/misc/genwqe/card_utils.c
@@ -590,6 +590,8 @@ int genwqe_user_vmap(struct genwqe_dev *cd, struct dma_mapping *m, void *uaddr,
 				 m->nr_pages,
 				 1,		/* write by caller */
 				 m->page_list);	/* ptrs to pages */
+	if (rc < 0)
+		goto fail_get_user_pages;
 
 	/* assumption: get_user_pages can be killed by signals. */
 	if (rc < m->nr_pages) {
-- 
2.1.1

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