2024-02-06 17:03:38

by Kees Cook

Subject: [PATCH] xen/gntalloc: Replace UAPI 1-element array

Without changing the structure size (since it is UAPI), add a proper
flexible array member, and reference it in the kernel so that it will
not be trip the array-bounds sanitizer[1].

Link: https://github.com/KSPP/linux/issues/113 [1]
Cc: Juergen Gross <[email protected]>
Cc: Stefano Stabellini <[email protected]>
Cc: Oleksandr Tyshchenko <[email protected]>
Cc: Gustavo A. R. Silva <[email protected]>
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
drivers/xen/gntalloc.c | 2 +-
include/uapi/xen/gntalloc.h | 5 ++++-
2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
index 26ffb8755ffb..f93f73ecefee 100644
--- a/drivers/xen/gntalloc.c
+++ b/drivers/xen/gntalloc.c
@@ -317,7 +317,7 @@ static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
rc = -EFAULT;
goto out_free;
}
- if (copy_to_user(arg->gref_ids, gref_ids,
+ if (copy_to_user(arg->gref_ids_flex, gref_ids,
sizeof(gref_ids[0]) * op.count)) {
rc = -EFAULT;
goto out_free;
diff --git a/include/uapi/xen/gntalloc.h b/include/uapi/xen/gntalloc.h
index 48d2790ef928..3109282672f3 100644
--- a/include/uapi/xen/gntalloc.h
+++ b/include/uapi/xen/gntalloc.h
@@ -31,7 +31,10 @@ struct ioctl_gntalloc_alloc_gref {
__u64 index;
/* The grant references of the newly created grant, one per page */
/* Variable size, depending on count */
- __u32 gref_ids[1];
+ union {
+ __u32 gref_ids[1];
+ __DECLARE_FLEX_ARRAY(__u32, gref_ids_flex);
+ };
};

#define GNTALLOC_FLAG_WRITABLE 1
--
2.34.1

2024-02-06 17:06:54

by Gustavo A. R. Silva

Subject: Re: [PATCH] xen/gntalloc: Replace UAPI 1-element array

On 2/6/24 11:03, Kees Cook wrote:
> Without changing the structure size (since it is UAPI), add a proper
> flexible array member, and reference it in the kernel so that it will
> not be trip the array-bounds sanitizer[1].
>
> Link: https://github.com/KSPP/linux/issues/113 [1]
> Cc: Juergen Gross <[email protected]>
> Cc: Stefano Stabellini <[email protected]>
> Cc: Oleksandr Tyshchenko <[email protected]>
> Cc: Gustavo A. R. Silva <[email protected]>
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>

Reviewed-by: Gustavo A. R. Silva <[email protected]>

Thanks!
--
Gustavo

> ---
> drivers/xen/gntalloc.c | 2 +-
> include/uapi/xen/gntalloc.h | 5 ++++-
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
> index 26ffb8755ffb..f93f73ecefee 100644
> --- a/drivers/xen/gntalloc.c
> +++ b/drivers/xen/gntalloc.c
> @@ -317,7 +317,7 @@ static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
> rc = -EFAULT;
> goto out_free;
> }
> - if (copy_to_user(arg->gref_ids, gref_ids,
> + if (copy_to_user(arg->gref_ids_flex, gref_ids,
> sizeof(gref_ids[0]) * op.count)) {
> rc = -EFAULT;
> goto out_free;
> diff --git a/include/uapi/xen/gntalloc.h b/include/uapi/xen/gntalloc.h
> index 48d2790ef928..3109282672f3 100644
> --- a/include/uapi/xen/gntalloc.h
> +++ b/include/uapi/xen/gntalloc.h
> @@ -31,7 +31,10 @@ struct ioctl_gntalloc_alloc_gref {
> __u64 index;
> /* The grant references of the newly created grant, one per page */
> /* Variable size, depending on count */
> - __u32 gref_ids[1];
> + union {
> + __u32 gref_ids[1];
> + __DECLARE_FLEX_ARRAY(__u32, gref_ids_flex);
> + };
> };
>
> #define GNTALLOC_FLAG_WRITABLE 1