2024-05-13 23:46:22

by Bill Wendling

Subject: [PATCH] hpfs: Annotate struct hpfs_dirent with __counted_by

Prepare for the coming implementation by GCC and Clang of the
__counted_by attribute. Flexible array members annotated with
__counted_by can have their accesses bounds-checked at run-time checking
via CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE
(for strcpy/memcpy-family functions).

Cc: Mikulas Patocka <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: "Gustavo A. R. Silva" <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Justin Stitt <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Bill Wendling <[email protected]>
---
fs/hpfs/hpfs.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/hpfs/hpfs.h b/fs/hpfs/hpfs.h
index 281dec8f636b..ac137787f1f9 100644
--- a/fs/hpfs/hpfs.h
+++ b/fs/hpfs/hpfs.h
@@ -357,7 +357,7 @@ struct hpfs_dirent {
u8 ix; /* code page index (of filename), see
struct code_page_data */
u8 namelen; /* file name length */
- u8 name[]; /* file name */
+ u8 name[] __counted_by(namelen); /* file name */
/* dnode_secno down; btree down pointer, if present,
follows name on next word boundary, or maybe it
precedes next dirent, which is on a word boundary. */
--
2.45.0.rc1.225.g2a3ae87e7f-goog

2024-05-14 01:29:47

by Kees Cook

Subject: Re: [PATCH] hpfs: Annotate struct hpfs_dirent with __counted_by

On Mon, May 13, 2024 at 04:45:54PM -0700, Bill Wendling wrote:
> Prepare for the coming implementation by GCC and Clang of the
> __counted_by attribute. Flexible array members annotated with
> __counted_by can have their accesses bounds-checked at run-time checking
> via CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE
> (for strcpy/memcpy-family functions).
>
> Cc: Mikulas Patocka <[email protected]>
> Cc: Kees Cook <[email protected]>
> Cc: "Gustavo A. R. Silva" <[email protected]>
> Cc: Nathan Chancellor <[email protected]>
> Cc: Nick Desaulniers <[email protected]>
> Cc: Justin Stitt <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Bill Wendling <[email protected]>
> ---
> fs/hpfs/hpfs.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/hpfs/hpfs.h b/fs/hpfs/hpfs.h
> index 281dec8f636b..ac137787f1f9 100644
> --- a/fs/hpfs/hpfs.h
> +++ b/fs/hpfs/hpfs.h
> @@ -357,7 +357,7 @@ struct hpfs_dirent {
> u8 ix; /* code page index (of filename), see
> struct code_page_data */
> u8 namelen; /* file name length */
> - u8 name[]; /* file name */
> + u8 name[] __counted_by(namelen); /* file name */
> /* dnode_secno down; btree down pointer, if present,
> follows name on next word boundary, or maybe it
> precedes next dirent, which is on a word boundary. */

Looking through struct hpfs_dirent::name uses, I think everything checks
out. I do see some confusing manipulations in hpfs_add_de(), though. I
*think* it'll be okay, though.

Reviewed-by: Kees Cook <[email protected]>

--
Kees Cook