linux-kernel - Re: [PATCH v9 1/4] reiserfs: Add security prefix to xattr name in reiserfs_security

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Message-ID: <CAHC9VhRg7twUWXLH0xTaWc2MeSFExkGr9tJztYopzD0JEM-npw@mail.gmail.com>
Date:   Thu, 30 Mar 2023 17:15:40 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     zohar@...ux.ibm.com, dmitry.kasatkin@...il.com, jmorris@...ei.org,
        serge@...lyn.com, stephen.smalley.work@...il.com,
        eparis@...isplace.org, casey@...aufler-ca.com,
        reiserfs-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        bpf@...r.kernel.org, kpsingh@...nel.org, keescook@...omium.org,
        nicolas.bouchinet@...p-os.org,
        Roberto Sassu <roberto.sassu@...wei.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v9 1/4] reiserfs: Add security prefix to xattr name in reiserfs_security_write()

On Wed, Mar 29, 2023 at 9:05 AM Roberto Sassu
<roberto.sassu@...weicloud.com> wrote:
> From: Roberto Sassu <roberto.sassu@...wei.com>
>
> Reiserfs sets a security xattr at inode creation time in two stages: first,
> it calls reiserfs_security_init() to obtain the xattr from active LSMs;
> then, it calls reiserfs_security_write() to actually write that xattr.
>
> Unfortunately, it seems there is a wrong expectation that LSMs provide the
> full xattr name in the form 'security.<suffix>'. However, LSMs always
> provided just the suffix, causing reiserfs to not write the xattr at all
> (if the suffix is shorter than the prefix), or to write an xattr with the
> wrong name.
>
> Add a temporary buffer in reiserfs_security_write(), and write to it the
> full xattr name, before passing it to reiserfs_xattr_set_handle().
>
> Since the 'security.' prefix is always prepended, remove the name length
> check.
>
> Cc: stable@...r.kernel.org # v2.6.x
> Fixes: 57fe60df6241 ("reiserfs: add atomic addition of selinux attributes during inode creation")
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---
>  fs/reiserfs/xattr_security.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/fs/reiserfs/xattr_security.c b/fs/reiserfs/xattr_security.c
> index 6bffdf9a4fd..b0c354ab113 100644
> --- a/fs/reiserfs/xattr_security.c
> +++ b/fs/reiserfs/xattr_security.c
> @@ -95,11 +95,13 @@ int reiserfs_security_write(struct reiserfs_transaction_handle *th,
>                             struct inode *inode,
>                             struct reiserfs_security_handle *sec)
>  {
> +       char xattr_name[XATTR_NAME_MAX + 1];
>         int error;
> -       if (strlen(sec->name) < sizeof(XATTR_SECURITY_PREFIX))
> -               return -EINVAL;

If one really wanted to be paranoid they could verify that
'XATTR_SECURITY_PREFIX_LEN + strlen(sec->name) <= XATTR_NAME_MAX' and
return EINVAL, but that really shouldn't be an issue and if the
concatenation does result in a xattr name that is too big, the
snprintf() will safely truncate/managle it.

Regardless, this patch is fine with me, but it would be nice if at
least of the reiserfs/VFS folks could provide an ACK/Reviewed-by tag,
although I think we can still move forward on this without one of
those.

> -       error = reiserfs_xattr_set_handle(th, inode, sec->name, sec->value,
> +       snprintf(xattr_name, sizeof(xattr_name), "%s%s", XATTR_SECURITY_PREFIX,
> +                sec->name);
> +
> +       error = reiserfs_xattr_set_handle(th, inode, xattr_name, sec->value,
>                                           sec->length, XATTR_CREATE);
>         if (error == -ENODATA || error == -EOPNOTSUPP)
>                 error = 0;
> --
> 2.25.1

-- 
paul-moore.com