LinuxLists.cc - [PATCH][next] btrfs: Add __counted_by for struct btrfs_delayed_item and use struct

2023-10-09 20:45:21

Subject: [PATCH][next] btrfs: Add __counted_by for struct btrfs_delayed_item and use struct_size()

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 via CONFIG_UBSAN_BOUNDS (for
array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

While there, use struct_size() helper, instead of the open-coded
version, to calculate the size for the allocation of the whole
flexible structure, including of course, the flexible-array member.

This code was found with the help of Coccinelle, and audited and
fixed manually.

Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
fs/btrfs/delayed-inode.c | 2 +-
fs/btrfs/delayed-inode.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 35d7616615c1..4f364e242341 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -313,7 +313,7 @@ static struct btrfs_delayed_item *btrfs_alloc_delayed_item(u16 data_len,
{
struct btrfs_delayed_item *item;

- item = kmalloc(sizeof(*item) + data_len, GFP_NOFS);
+ item = kmalloc(struct_size(item, data, data_len), GFP_NOFS);
if (item) {
item->data_len = data_len;
item->type = type;
diff --git a/fs/btrfs/delayed-inode.h b/fs/btrfs/delayed-inode.h
index d050e572c7f9..5cceb31bbd16 100644
--- a/fs/btrfs/delayed-inode.h
+++ b/fs/btrfs/delayed-inode.h
@@ -95,7 +95,7 @@ struct btrfs_delayed_item {
bool logged;
/* The maximum leaf size is 64K, so u16 is more than enough. */
u16 data_len;
- char data[];
+ char data[] __counted_by(data_len);
};

static inline void btrfs_init_delayed_root(
--
2.34.1

2023-10-09 21:11:13

by Kees Cook

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Subject: Re: [PATCH][next] btrfs: Add __counted_by for struct btrfs_delayed_item and use struct_size()

On Mon, Oct 09, 2023 at 02:44:54PM -0600, Gustavo A. R. Silva 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 via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> While there, use struct_size() helper, instead of the open-coded
> version, to calculate the size for the allocation of the whole
> flexible structure, including of course, the flexible-array member.
>
> This code was found with the help of Coccinelle, and audited and
> fixed manually.
>
> Signed-off-by: Gustavo A. R. Silva <[email protected]>

Looks right to me.

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

--
Kees Cook

2023-10-09 22:57:36

by David Sterba

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