On Mon, May 22, 2023 at 2:39 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> 1-element arrays are deprecated, and are being replaced with C99
> flexible arrays[1]. In the future, we can add annotations for the
> flexible array member "encrypted_path" to have a size determined
> by the "len" member.
>
> As sizes were being calculated with the extra byte intentionally,
> propagate the difference so there is no change in binary output.
>
> [1] https://github.com/KSPP/linux/issues/79
>
> Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
> Cc: "Theodore Y. Ts'o" <tytso@xxxxxxx>
> Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> Cc: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> Cc: linux-fscrypt@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-By: Bill Wendling <morbo@xxxxxxxxxx>
(With a tear in my eye about the original code...)
> ---
> fs/crypto/fscrypt_private.h | 2 +-
> fs/crypto/hooks.c | 10 +++++-----
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
> index 7ab5a7b7eef8..2d63da48635a 100644
> --- a/fs/crypto/fscrypt_private.h
> +++ b/fs/crypto/fscrypt_private.h
> @@ -171,7 +171,7 @@ fscrypt_policy_flags(const union fscrypt_policy *policy)
> */
> struct fscrypt_symlink_data {
> __le16 len;
> - char encrypted_path[1];
> + char encrypted_path[];
> } __packed;
>
> /**
> diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
> index 9e786ae66a13..6238dbcadcad 100644
> --- a/fs/crypto/hooks.c
> +++ b/fs/crypto/hooks.c
> @@ -255,10 +255,10 @@ int fscrypt_prepare_symlink(struct inode *dir, const char *target,
> * for now since filesystems will assume it is there and subtract it.
> */
> if (!__fscrypt_fname_encrypted_size(policy, len,
> - max_len - sizeof(struct fscrypt_symlink_data),
> + max_len - sizeof(struct fscrypt_symlink_data) - 1,
> &disk_link->len))
> return -ENAMETOOLONG;
> - disk_link->len += sizeof(struct fscrypt_symlink_data);
> + disk_link->len += sizeof(struct fscrypt_symlink_data) + 1;
>
> disk_link->name = NULL;
> return 0;
> @@ -289,7 +289,7 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
> if (!sd)
> return -ENOMEM;
> }
> - ciphertext_len = disk_link->len - sizeof(*sd);
> + ciphertext_len = disk_link->len - sizeof(*sd) - 1;
> sd->len = cpu_to_le16(ciphertext_len);
>
> err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path,
> @@ -367,7 +367,7 @@ const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
> * the ciphertext length, even though this is redundant with i_size.
> */
>
> - if (max_size < sizeof(*sd))
> + if (max_size < sizeof(*sd) + 1)
> return ERR_PTR(-EUCLEAN);
> sd = caddr;
> cstr.name = (unsigned char *)sd->encrypted_path;
> @@ -376,7 +376,7 @@ const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
> if (cstr.len == 0)
> return ERR_PTR(-EUCLEAN);
>
> - if (cstr.len + sizeof(*sd) - 1 > max_size)
> + if (cstr.len + sizeof(*sd) > max_size)
> return ERR_PTR(-EUCLEAN);
>
> err = fscrypt_fname_alloc_buffer(cstr.len, &pstr);
> --
> 2.34.1
>
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