Re: [PATCH] fs/ntfs3: validate that EA entry size covers its name and value

[Konstantin Komarov <almaz.alexandrovich@paragon-software.com>]

On 7/24/26 00:10, Your Name wrote:

> From: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
>
> ntfs_read_ea() walks the on-disk $EA attribute and checks each EA_FULL
> entry for consistency.  For an entry with a non-zero ef->size (the
> offset to the next entry) the loop only verifies that this stride fits
> in the remaining buffer, and then continues:
>
>          if (ef->size) {
>                  ea_size = le32_to_cpu(ef->size);
>                  if (ea_size > bytes)
>                          goto out1;
>                  continue;
>          }
>
> It never verifies that the entry's own name (ef->name_len) and value
> (ef->elength) actually fit inside ef->size.  A later reader trusts
> ef->elength unconditionally; ntfs_get_ea() does:
>
>          len = le16_to_cpu(ea->elength);         /* up to 0xffff */
>          ...
>          if (len > size)                         /* size is the user buffer */
>                  return -ERANGE;
>          memcpy(buffer, ea->name + ea->name_len + 1, len);
>
> A crafted image with a small but valid ef->size (e.g. 24) and
> ef->elength == 0xffff therefore passes validation, and a getxattr()
> with a large enough user buffer copies up to 64 KiB starting just past
> the short entry -- an out-of-bounds read of the ea_all allocation that
> leaks adjacent kernel heap memory to userspace.
>
>    BUG: KASAN: slab-out-of-bounds in ntfs_get_ea+0x2b8/0x3f0
>    Read of size 65535 ...
>     ntfs_get_ea -> ntfs_getxattr -> vfs_getxattr -> do_getxattr
>
> The zero-ef->size branch already computes the same struct_size() to
> derive the stride; mirror that in the non-zero branch and reject the
> entry when its declared size cannot hold the name and value.
>
> Fixes: 0e8235d28f3a ("fs/ntfs3: Check fields while reading")
> Cc: stable@vger.kernel.org
> Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
> ---
>   fs/ntfs3/xattr.c | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
>
> diff --git a/fs/ntfs3/xattr.c b/fs/ntfs3/xattr.c
> index 04814dd29375..57114fb726f7 100644
> --- a/fs/ntfs3/xattr.c
> +++ b/fs/ntfs3/xattr.c
> @@ -155,6 +155,24 @@ static int ntfs_read_ea(struct ntfs_inode *ni, struct EA_FULL **ea,
>                          ea_size = le32_to_cpu(ef->size);
>                          if (ea_size > bytes)
>                                  goto out1;
> +
> +                       /* Check if we can use fields ef->name_len and ef->elength. */
> +                       if (bytes < offsetof(struct EA_FULL, name))
> +                               goto out1;
> +
> +                       /*
> +                        * The declared entry size (ef->size) must be large
> +                        * enough to hold the name and value.  Otherwise a later
> +                        * reader such as ntfs_get_ea() copies ef->elength bytes
> +                        * starting past the entry, reading out of bounds of the
> +                        * ea buffer and leaking adjacent heap memory to
> +                        * userspace via getxattr().
> +                        */
> +                       if (struct_size(ef, name,
> +                                       1 + ef->name_len +
> +                                               le16_to_cpu(ef->elength)) >
> +                           ea_size)
> +                               goto out1;
>                          continue;
>                  }
>
> --
> 2.43.0

Hello,

Your patch was applied, thank you.

Regards,
Konstantin