Re: [PATCH 3/3] Smack: remove unneeded NULL-termination from securtity label

From: Serge E. Hallyn
Date: Fri Aug 08 2014 - 17:17:24 EST


Quoting Konstantin Khlebnikov (k.khlebnikov@xxxxxxxxxxx):
> Values of extended attributes are stored as binary blobs. NULL-termination
> of them isn't required. It just wastes disk space and confuses command-line
> tools like getfattr because they have to print that zero byte at the end.
>
> This patch removes terminating zero byte from initial security label in
> smack_inode_init_security and cuts it out in function smack_inode_getsecurity
> which is used by syscall getxattr. This change seems completely safe, because
> function smk_parse_smack ignores everything after first zero byte.
>
> Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@xxxxxxxxxxx>

selinux doesn't seem to do it this way, and apparmor doesn't use these
at all, but your reasoning does seem correct.

Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>

> ---
> security/smack/smack_lsm.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index afa5ad0..16ae853 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -672,7 +672,7 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
> }
>
> if (len)
> - *len = strlen(isp) + 1;
> + *len = strlen(isp);
>
> return 0;
> }
> @@ -1076,7 +1076,7 @@ static int smack_inode_getsecurity(const struct inode *inode,
>
> if (strcmp(name, XATTR_SMACK_SUFFIX) == 0) {
> isp = smk_of_inode(inode);
> - ilen = strlen(isp) + 1;
> + ilen = strlen(isp);
> *buffer = isp;
> return ilen;
> }
> @@ -1101,7 +1101,7 @@ static int smack_inode_getsecurity(const struct inode *inode,
> else
> return -EOPNOTSUPP;
>
> - ilen = strlen(isp) + 1;
> + ilen = strlen(isp);
> if (rc == 0) {
> *buffer = isp;
> rc = ilen;
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