2021-08-11 17:55:13

by Pavel Skripkin

Subject: [PATCH next] udmabuf: fix general protection fault in udmabuf_create

Syzbot reported general protection fault in udmabuf_create. The problem
was in wrong error handling.

In commit 16c243e99d33 ("udmabuf: Add support for mapping hugepages (v4)")
shmem_read_mapping_page() call was replaced with find_get_page_flags(),
but find_get_page_flags() returns NULL on failure instead PTR_ERR().

Wrong error checking was causing GPF in get_page(), since passed page
was equal to NULL. Fix it by changing if (IS_ER(!hpage)) to if (!hpage)

Reported-by: [email protected]
Fixes: 16c243e99d33 ("udmabuf: Add support for mapping hugepages (v4)")
Signed-off-by: Pavel Skripkin <[email protected]>
---
drivers/dma-buf/udmabuf.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 8df761a10251..c57a609db75b 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -227,8 +227,8 @@ static long udmabuf_create(struct miscdevice *device,
if (!hpage) {
hpage = find_get_page_flags(mapping, pgoff,
FGP_ACCESSED);
- if (IS_ERR(hpage)) {
- ret = PTR_ERR(hpage);
+ if (!hpage) {
+ ret = -EINVAL;
goto err;
}
}
--
2.32.0

2021-08-12 07:47:25

by Gerd Hoffmann

Subject: Re: [PATCH next] udmabuf: fix general protection fault in udmabuf_create

On Wed, Aug 11, 2021 at 08:50:52PM +0300, Pavel Skripkin wrote:
> Syzbot reported general protection fault in udmabuf_create. The problem
> was in wrong error handling.
>
> In commit 16c243e99d33 ("udmabuf: Add support for mapping hugepages (v4)")
> shmem_read_mapping_page() call was replaced with find_get_page_flags(),
> but find_get_page_flags() returns NULL on failure instead PTR_ERR().
>
> Wrong error checking was causing GPF in get_page(), since passed page
> was equal to NULL. Fix it by changing if (IS_ER(!hpage)) to if (!hpage)
>
> Reported-by: [email protected]
> Fixes: 16c243e99d33 ("udmabuf: Add support for mapping hugepages (v4)")
> Signed-off-by: Pavel Skripkin <[email protected]>

Pushed to drm-misc-next.

thanks,
Gerd