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SubjectRe: [PATCH v3 09/12] ima: add ima_inode_setxattr/removexattr function and calls
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On Wed, Mar 21, 2012 at 8:54 PM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
> Based on xattr_permission comments, the restriction to modify 'security'
> xattr is left up to the underlying fs or lsm. Ensure that not just anyone
> can modify or remove 'security.ima'.
>
> Changelog v1:
> - Unless IMA-APPRAISE is configured, use stub ima_inode_removexattr()/setxattr()
>  functions.  (Moved ima_inode_removexattr()/setxattr() to ima_appraise.c)
>
> Changelog:
>  - take i_mutex to fix locking (Dmitry Kasatkin)
>  - ima_reset_appraise_flags should only be called when modifying or
>    removing the 'security.ima' xattr. Requires CAP_SYS_ADMIN privilege.
>    (Incorporated fix from Roberto Sassu)
>  - Even if allowed to update security.ima, reset the appraisal flags,
>    forcing re-appraisal.
>  - Replace CAP_MAC_ADMIN with CAP_SYS_ADMIN
>  - static inline ima_inode_setxattr()/ima_inode_removexattr() stubs
>  - ima_protect_xattr should be static
>
> Signed-off-by: Mimi Zohar <zohar@us.ibm.com>

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>

> ---
>  include/linux/ima.h                   |   17 ++++++++++
>  security/integrity/ima/ima_appraise.c |   57 +++++++++++++++++++++++++++++++++
>  security/security.c                   |    6 +++
>  3 files changed, 80 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index e2bfbb1..2c7223d 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -44,10 +44,27 @@ static inline int ima_file_mmap(struct file *file, unsigned long prot)
>
>  #ifdef CONFIG_IMA_APPRAISE
>  extern void ima_inode_post_setattr(struct dentry *dentry);
> +extern int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
> +                      const void *xattr_value, size_t xattr_value_len);
> +extern int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name);
>  #else
>  static inline void ima_inode_post_setattr(struct dentry *dentry)
>  {
>        return;
>  }
> +
> +static inline int ima_inode_setxattr(struct dentry *dentry,
> +                                    const char *xattr_name,
> +                                    const void *xattr_value,
> +                                    size_t xattr_value_len)
> +{
> +       return 0;
> +}
> +
> +static inline int ima_inode_removexattr(struct dentry *dentry,
> +                                       const char *xattr_name)
> +{
> +       return 0;
> +}
>  #endif /* CONFIG_IMA_APPRAISE_H */
>  #endif /* _LINUX_IMA_H */
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 681cb6e..becc7e0 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -169,3 +169,60 @@ void ima_inode_post_setattr(struct dentry *dentry)
>                rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
>        return;
>  }
> +
> +/*
> + * ima_protect_xattr - protect 'security.ima'
> + *
> + * Ensure that not just anyone can modify or remove 'security.ima'.
> + */
> +static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
> +                            const void *xattr_value, size_t xattr_value_len)
> +{
> +       if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
> +               if (!capable(CAP_SYS_ADMIN))
> +                       return -EPERM;
> +               return 1;
> +       }
> +       return 0;
> +}
> +
> +static void ima_reset_appraise_flags(struct inode *inode)
> +{
> +       struct integrity_iint_cache *iint;
> +
> +       if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode))
> +               return;
> +
> +       iint = integrity_iint_find(inode);
> +       if (!iint)
> +               return;
> +
> +       iint->flags &= ~(IMA_COLLECTED | IMA_APPRAISED | IMA_MEASURED);
> +       return;
> +}
> +
> +int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
> +                      const void *xattr_value, size_t xattr_value_len)
> +{
> +       int result;
> +
> +       result = ima_protect_xattr(dentry, xattr_name, xattr_value,
> +                                  xattr_value_len);
> +       if (result == 1) {
> +               ima_reset_appraise_flags(dentry->d_inode);
> +               result = 0;
> +       }
> +       return result;
> +}
> +
> +int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
> +{
> +       int result;
> +
> +       result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
> +       if (result == 1) {
> +               ima_reset_appraise_flags(dentry->d_inode);
> +               result = 0;
> +       }
> +       return result;
> +}
> diff --git a/security/security.c b/security/security.c
> index e50bbf4..7bb127e 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -557,6 +557,9 @@ int security_inode_setxattr(struct dentry *dentry, const char *name,
>        ret = security_ops->inode_setxattr(dentry, name, value, size, flags);
>        if (ret)
>                return ret;
> +       ret = ima_inode_setxattr(dentry, name, value, size);
> +       if (ret)
> +               return ret;
>        return evm_inode_setxattr(dentry, name, value, size);
>  }
>
> @@ -592,6 +595,9 @@ int security_inode_removexattr(struct dentry *dentry, const char *name)
>        ret = security_ops->inode_removexattr(dentry, name);
>        if (ret)
>                return ret;
> +       ret = ima_inode_removexattr(dentry, name);
> +       if (ret)
> +               return ret;
>        return evm_inode_removexattr(dentry, name);
>  }
>
> --
> 1.7.6.5
>
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