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 <[email protected]>
Signed-off-by: Roberto Sassu <[email protected]>
---
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);
+}
+
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);
+}
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);
}
--
2.26.2
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 <[email protected]>
> Signed-off-by: Roberto Sassu <[email protected]>
> ---
> 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);
> }
>
> From: Casey Schaufler [mailto:[email protected]]
> Sent: Wednesday, April 7, 2021 6:18 PM
> 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 <[email protected]>
> > Signed-off-by: Roberto Sassu <[email protected]>
> > ---
> > 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?
Hi Casey
I would expect that this does not have a significant impact on
the performance (it is just a strcmp on the xattr name).
Thanks
Roberto
HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli
> > 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);
> > }
> >
On Wed, 2021-04-07 at 09:17 -0700, Casey Schaufler wrote:
> > 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?
The first time the call to ima_protect_xattr() prevents the
security.ima from being inappropriately modified. The second time it
resets the cached status flags. From a performance perspective,
unnecessarily re-calcuating the file hash is worse than rechecking the
security xattr string.
Mimi