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Message-ID: <d4aba724-2935-467b-e57c-cd961112190b@schaufler-ca.com>
Date: Wed, 7 Apr 2021 09:17:48 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: Roberto Sassu <roberto.sassu@...wei.com>, zohar@...ux.ibm.com,
mjg59@...gle.com
Cc: linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v5 04/12] ima: Move ima_reset_appraise_flags() call to
post hooks
On 4/7/2021 3:52 AM, Roberto Sassu wrote:
> ima_inode_setxattr() and ima_inode_removexattr() hooks are called before an
> operation is performed. Thus, ima_reset_appraise_flags() should not be
> called there, as flags might be unnecessarily reset if the operation is
> denied.
>
> This patch introduces the post hooks ima_inode_post_setxattr() and
> ima_inode_post_removexattr(), and adds the call to
> ima_reset_appraise_flags() in the new functions.
>
> Cc: Casey Schaufler <casey@...aufler-ca.com>
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---
> fs/xattr.c | 2 ++
> include/linux/ima.h | 18 ++++++++++++++++++
> security/integrity/ima/ima_appraise.c | 25 ++++++++++++++++++++++---
> security/security.c | 1 +
> 4 files changed, 43 insertions(+), 3 deletions(-)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index b3444e06cded..81847f132d26 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -16,6 +16,7 @@
> #include <linux/namei.h>
> #include <linux/security.h>
> #include <linux/evm.h>
> +#include <linux/ima.h>
> #include <linux/syscalls.h>
> #include <linux/export.h>
> #include <linux/fsnotify.h>
> @@ -502,6 +503,7 @@ __vfs_removexattr_locked(struct user_namespace *mnt_userns,
>
> if (!error) {
> fsnotify_xattr(dentry);
> + ima_inode_post_removexattr(dentry, name);
> evm_inode_post_removexattr(dentry, name);
> }
>
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 61d5723ec303..5e059da43857 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -171,7 +171,13 @@ extern void ima_inode_post_setattr(struct user_namespace *mnt_userns,
> 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 void ima_inode_post_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);
> +extern void ima_inode_post_removexattr(struct dentry *dentry,
> + const char *xattr_name);
> #else
> static inline bool is_ima_appraise_enabled(void)
> {
> @@ -192,11 +198,23 @@ static inline int ima_inode_setxattr(struct dentry *dentry,
> return 0;
> }
>
> +static inline void ima_inode_post_setxattr(struct dentry *dentry,
> + const char *xattr_name,
> + const void *xattr_value,
> + size_t xattr_value_len)
> +{
> +}
> +
> static inline int ima_inode_removexattr(struct dentry *dentry,
> const char *xattr_name)
> {
> return 0;
> }
> +
> +static inline void ima_inode_post_removexattr(struct dentry *dentry,
> + const char *xattr_name)
> +{
> +}
> #endif /* CONFIG_IMA_APPRAISE */
>
> #if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING)
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 565e33ff19d0..1f029e4c8d7f 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -577,21 +577,40 @@ int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
> if (result == 1) {
> if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
> return -EINVAL;
> - ima_reset_appraise_flags(d_backing_inode(dentry),
> - xvalue->type == EVM_IMA_XATTR_DIGSIG);
> result = 0;
> }
> return result;
> }
>
> +void ima_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
> + const void *xattr_value, size_t xattr_value_len)
> +{
> + const struct evm_ima_xattr_data *xvalue = xattr_value;
> + int result;
> +
> + result = ima_protect_xattr(dentry, xattr_name, xattr_value,
> + xattr_value_len);
> + if (result == 1)
> + ima_reset_appraise_flags(d_backing_inode(dentry),
> + xvalue->type == EVM_IMA_XATTR_DIGSIG);
> +}
> +
Now you're calling ima_protect_xattr() twice for each setxattr.
Is that safe? Is it performant? Does it matter?
> 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(d_backing_inode(dentry), 0);
> result = 0;
> }
> return result;
> }
> +
> +void ima_inode_post_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(d_backing_inode(dentry), 0);
> +}
Now you're calling ima_protect_xattr() twice for each removexattr.
Is that safe? Is it performant? Does it matter?
> diff --git a/security/security.c b/security/security.c
> index 5ac96b16f8fa..efb1f874dc41 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1319,6 +1319,7 @@ void security_inode_post_setxattr(struct dentry *dentry, const char *name,
> if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
> return;
> call_void_hook(inode_post_setxattr, dentry, name, value, size, flags);
> + ima_inode_post_setxattr(dentry, name, value, size);
> evm_inode_post_setxattr(dentry, name, value, size);
> }
>
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