On Tue, Jul 30, 2024 at 07:23:04PM +0200, Thorsten Blum wrote:
> Add the __counted_by compiler attribute to the flexible array member
> inodes to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE.
>
> Remove the now obsolete comment on the count field.
>
> Refactor ext4_expand_inode_array() by assigning count before copying any
> data using memcpy(). Copy only the inodes array instead of the whole
> struct because count has been set explicitly.
>
> Use struct_size() and struct_size_t() instead of offsetof().
>
> Change the data type of the local variable count to unsigned int to
> match the struct's count data type.
>
> Compile-tested only.
>
> Signed-off-by: Thorsten Blum <thorsten.b...@toblux.com>
> ---
> Changes in v2:
> - Adjust ext4_expand_inode_array() as suggested by Gustavo A. R. Silva
> - Use struct_size() and struct_size_t() instead of offsetof()
> - Link to v1:
> https://lore.kernel.org/linux-kernel/20240729110454.346918-3-thorsten.b...@toblux.com/
> ---
> fs/ext4/xattr.c | 20 +++++++++-----------
> fs/ext4/xattr.h | 4 ++--
> 2 files changed, 11 insertions(+), 13 deletions(-)
>
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 46ce2f21fef9..b27543587103 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -2879,11 +2879,10 @@ ext4_expand_inode_array(struct ext4_xattr_inode_array
> **ea_inode_array,
> if (*ea_inode_array == NULL) {
> /*
> * Start with 15 inodes, so it fits into a power-of-two size.
> - * If *ea_inode_array is NULL, this is essentially offsetof()
> */
> (*ea_inode_array) =
> - kmalloc(offsetof(struct ext4_xattr_inode_array,
> - inodes[EIA_MASK]),
> + kmalloc(struct_size_t(struct ext4_xattr_inode_array,
This can be struct_size(*ea_inode_array, ...) too, like you have below.
> + inodes, EIA_MASK),
> GFP_NOFS);
> if (*ea_inode_array == NULL)
> return -ENOMEM;
> @@ -2891,17 +2890,16 @@ ext4_expand_inode_array(struct ext4_xattr_inode_array
> **ea_inode_array,
> } else if (((*ea_inode_array)->count & EIA_MASK) == EIA_MASK) {
> /* expand the array once all 15 + n * 16 slots are full */
> struct ext4_xattr_inode_array *new_array = NULL;
> - int count = (*ea_inode_array)->count;
> + unsigned int count = (*ea_inode_array)->count;
>
> - /* if new_array is NULL, this is essentially offsetof() */
> - new_array = kmalloc(
> - offsetof(struct ext4_xattr_inode_array,
> - inodes[count + EIA_INCR]),
> - GFP_NOFS);
> + new_array = kmalloc(struct_size(*ea_inode_array, inodes,
> + count + EIA_INCR),
> + GFP_NOFS);
> if (new_array == NULL)
> return -ENOMEM;
> - memcpy(new_array, *ea_inode_array,
> - offsetof(struct ext4_xattr_inode_array, inodes[count]));
> + new_array->count = count;
> + memcpy(new_array->inodes, (*ea_inode_array)->inodes,
> + count * sizeof(struct inode *));
> kfree(*ea_inode_array);
> *ea_inode_array = new_array;
> }
> diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
> index bd97c4aa8177..e14fb19dc912 100644
> --- a/fs/ext4/xattr.h
> +++ b/fs/ext4/xattr.h
> @@ -130,8 +130,8 @@ struct ext4_xattr_ibody_find {
> };
>
> struct ext4_xattr_inode_array {
> - unsigned int count; /* # of used items in the array */
> - struct inode *inodes[];
> + unsigned int count;
> + struct inode *inodes[] __counted_by(count);
> };
>
> extern const struct xattr_handler ext4_xattr_user_handler;
Thanks for the reworking!
--
Kees Cook
