[v2] fscrypt: Replace 1-element array with flexible array

Commit Message

Kees Cook May 23, 2023, 4:55 p.m. UTC

1-element arrays are deprecated and are being replaced with C99
flexible arrays[1].

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 <[e-mail]>
Cc: "Theodore Y. Ts'o" <[e-mail]>
Cc: Jaegeuk Kim <[e-mail]>
Cc: Gustavo A. R. Silva <[e-mail]>
Cc: [e-mail]
Signed-off-by: Kees Cook <[e-mail]>
---
v2: update commit log to avoid mentioning "len" member.
v1: https://lore.kernel.org/lkml/[e-mail]/
---
 fs/crypto/fscrypt_private.h |  2 +-
 fs/crypto/hooks.c           | 10 +++++-----
 2 files changed, 6 insertions(+), 6 deletions(-)

Comments

Eric Biggers May 24, 2023, 2:55 a.m. UTC | #1

On Tue, May 23, 2023 at 09:55:02AM -0700, Kees Cook wrote:
> 1-element arrays are deprecated and are being replaced with C99
> flexible arrays[1].
> 
> 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 <[e-mail]>
> Cc: "Theodore Y. Ts'o" <[e-mail]>
> Cc: Jaegeuk Kim <[e-mail]>
> Cc: Gustavo A. R. Silva <[e-mail]>
> Cc: [e-mail]
> Signed-off-by: Kees Cook <[e-mail]>
> ---
> v2: update commit log to avoid mentioning "len" member.
> v1: https://lore.kernel.org/lkml/[e-mail]/
> ---
>  fs/crypto/fscrypt_private.h |  2 +-
>  fs/crypto/hooks.c           | 10 +++++-----
>  2 files changed, 6 insertions(+), 6 deletions(-)

Thanks, applied to
https://git.kernel.org/pub/scm/fs/fscrypt/linux.git/log/?h=for-next

- Eric

Patch

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);