linux-hardening - Re: [RESEND PATCH v4] ext4: Annotate struct ext4_xattr_inode_array with __counted

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Message-Id: <90467BBB-59F4-48C5-AD18-4FDDAE3CF321@toblux.com>
Date: Wed, 21 Aug 2024 01:17:19 +0200
From: Thorsten Blum <thorsten.blum@...lux.com>
To: tytso@....edu,
 adilger.kernel@...ger.ca,
 Kees Cook <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: linux-ext4@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [RESEND PATCH v4] ext4: Annotate struct ext4_xattr_inode_array
 with __counted_by()

On 13. Aug 2024, at 09:07, Thorsten Blum <thorsten.blum@...lux.com> 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.
> 
> In ext4_expand_inode_array(), use struct_size() instead of offsetof()
> and remove the local variable count. Increment the count field before
> adding a new inode to the inodes array.
> 
> Compile-tested only.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@...lux.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.blum@toblux.com/
> 
> Changes in v3:
> - Use struct_size() instead of struct_size_t() as suggested by Kees Cook
> - Remove the local variable count as suggested by Gustavo A. R. Silva
> - Increment count before adding a new inode as suggested by Gustavo
> - Link to v2: https://lore.kernel.org/linux-kernel/20240730172301.231867-4-thorsten.blum@toblux.com/
> 
> Changes in v4:
> - Remove unnecessary count assignment and adjust copying the whole
>  struct as suggested by Gustavo
> - Link to v3: https://lore.kernel.org/linux-kernel/20240730205509.323320-3-thorsten.blum@toblux.com/
> ---
> fs/ext4/xattr.c | 22 ++++++++++------------
> fs/ext4/xattr.h |  4 ++--
> 2 files changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 46ce2f21fef9..263567d4e13d 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -2879,33 +2879,31 @@ 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]),
> - GFP_NOFS);
> + (*ea_inode_array) = kmalloc(
> + struct_size(*ea_inode_array, inodes, EIA_MASK),
> + GFP_NOFS);
> if (*ea_inode_array == NULL)
> return -ENOMEM;
> (*ea_inode_array)->count = 0;
> } 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;
> 
> - /* if new_array is NULL, this is essentially offsetof() */
> new_array = kmalloc(
> - offsetof(struct ext4_xattr_inode_array,
> - inodes[count + EIA_INCR]),
> - GFP_NOFS);
> + struct_size(*ea_inode_array, inodes,
> +    (*ea_inode_array)->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]));
> +       struct_size(*ea_inode_array, inodes,
> +   (*ea_inode_array)->count));
> kfree(*ea_inode_array);
> *ea_inode_array = new_array;
> }
> - (*ea_inode_array)->inodes[(*ea_inode_array)->count++] = inode;
> + (*ea_inode_array)->count++;
> + (*ea_inode_array)->inodes[(*ea_inode_array)->count - 1] = inode;
> return 0;
> }
> 
> 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;
> -- 
> 2.46.0
> 

Could someone take another look at this?

Thanks,
Thorsten