diff mbox series

[v2,11/12] ima: Introduce template field evmsig and write to field sig as fallback

Message ID 20200904092643.20013-7-roberto.sassu@huawei.com
State New
Headers show
Series IMA/EVM fixes | expand

Commit Message

Roberto Sassu Sept. 4, 2020, 9:26 a.m. UTC
With the patch to accept EVM portable signatures when the
appraise_type=imasig requirement is specified in the policy, appraisal can
be successfully done even if the file does not have an IMA signature.

However, remote attestation would not see that a different signature type
was used, as only IMA signatures can be included in the measurement list.
This patch solves the issue by introducing the new template field 'evmsig'
to show EVM portable signatures and by including its value in the existing
field 'sig' if the IMA signature is not found.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
---
 Documentation/security/IMA-templates.rst  |  4 ++-
 security/integrity/ima/ima_template.c     |  2 ++
 security/integrity/ima/ima_template_lib.c | 39 ++++++++++++++++++++++-
 security/integrity/ima/ima_template_lib.h |  2 ++
 4 files changed, 45 insertions(+), 2 deletions(-)

Comments

Mimi Zohar Sept. 17, 2020, 2:25 p.m. UTC | #1
Hi Roberto,

On Fri, 2020-09-04 at 11:26 +0200, Roberto Sassu wrote:
> With the patch to accept EVM portable signatures when the
> appraise_type=imasig requirement is specified in the policy, appraisal can
> be successfully done even if the file does not have an IMA signature.
> 
> However, remote attestation would not see that a different signature type
> was used, as only IMA signatures can be included in the measurement list.
> This patch solves the issue by introducing the new template field 'evmsig'
> to show EVM portable signatures and by including its value in the existing
> field 'sig' if the IMA signature is not found.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> Suggested-by: Mimi Zohar <zohar@linux.ibm.com>

Thank you!   Just a minor comment below.

<snip>

> diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
> index c022ee9e2a4e..2c596c2a89cc 100644
> --- a/security/integrity/ima/ima_template_lib.c
> +++ b/security/integrity/ima/ima_template_lib.c
> 
> @@ -438,7 +439,7 @@ int ima_eventsig_init(struct ima_event_data *event_data,
>  	struct evm_ima_xattr_data *xattr_value = event_data->xattr_value;
>  
>  	if ((!xattr_value) || (xattr_value->type != EVM_IMA_XATTR_DIGSIG))
> -		return 0;
> +		return ima_eventevmsig_init(event_data, field_data);
>  
>  	return ima_write_template_field_data(xattr_value, event_data->xattr_len,
>  					     DATA_FMT_HEX, field_data);
> @@ -484,3 +485,39 @@ int ima_eventmodsig_init(struct ima_event_data *event_data,
>  	return ima_write_template_field_data(data, data_len, DATA_FMT_HEX,
>  					     field_data);
>  }
> +
> +/*
> + *  ima_eventevmsig_init - include the EVM portable signature as part of the
> + *  template data
> + */
> +int ima_eventevmsig_init(struct ima_event_data *event_data,
> +			 struct ima_field_data *field_data)
> +{
> +	struct evm_ima_xattr_data *xattr_data = NULL;
> +	int rc = 0;
> +
> +	if (!event_data->file)
> +		return 0;
> +
> +	if (!(file_inode(event_data->file)->i_opflags & IOP_XATTR))
> +		return 0;
> +
> +	rc = vfs_getxattr_alloc(file_dentry(event_data->file), XATTR_NAME_EVM,
> +				(char **)&xattr_data, 0, GFP_NOFS);
> +	if (rc <= 0) {
> +		if (!rc || rc == -ENODATA)
> +			return 0;
> +
> +		return rc;

We're including the EVM signature on a best effort basis to help with
attestation.  Do we really care why it failed?   Are we going to act on
it?

Mimi

> +	}
> +
> +	if (xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG) {
> +		kfree(xattr_data);
> +		return 0;
> +	}
> +
> +	rc = ima_write_template_field_data((char *)xattr_data, rc, DATA_FMT_HEX,
> +					   field_data);
> +	kfree(xattr_data);
> +	return rc;
> +}
Roberto Sassu Sept. 17, 2020, 3:05 p.m. UTC | #2
> From: Mimi Zohar [mailto:zohar@linux.ibm.com]
> Sent: Thursday, September 17, 2020 4:25 PM
> Hi Roberto,
> 
> On Fri, 2020-09-04 at 11:26 +0200, Roberto Sassu wrote:
> > With the patch to accept EVM portable signatures when the
> > appraise_type=imasig requirement is specified in the policy, appraisal can
> > be successfully done even if the file does not have an IMA signature.
> >
> > However, remote attestation would not see that a different signature
> type
> > was used, as only IMA signatures can be included in the measurement list.
> > This patch solves the issue by introducing the new template field 'evmsig'
> > to show EVM portable signatures and by including its value in the existing
> > field 'sig' if the IMA signature is not found.
> >
> > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
> 
> Thank you!   Just a minor comment below.
> 
> <snip>
> 
> > diff --git a/security/integrity/ima/ima_template_lib.c
> b/security/integrity/ima/ima_template_lib.c
> > index c022ee9e2a4e..2c596c2a89cc 100644
> > --- a/security/integrity/ima/ima_template_lib.c
> > +++ b/security/integrity/ima/ima_template_lib.c
> >
> > @@ -438,7 +439,7 @@ int ima_eventsig_init(struct ima_event_data
> *event_data,
> >  	struct evm_ima_xattr_data *xattr_value = event_data->xattr_value;
> >
> >  	if ((!xattr_value) || (xattr_value->type !=
> EVM_IMA_XATTR_DIGSIG))
> > -		return 0;
> > +		return ima_eventevmsig_init(event_data, field_data);
> >
> >  	return ima_write_template_field_data(xattr_value, event_data-
> >xattr_len,
> >  					     DATA_FMT_HEX, field_data);
> > @@ -484,3 +485,39 @@ int ima_eventmodsig_init(struct ima_event_data
> *event_data,
> >  	return ima_write_template_field_data(data, data_len,
> DATA_FMT_HEX,
> >  					     field_data);
> >  }
> > +
> > +/*
> > + *  ima_eventevmsig_init - include the EVM portable signature as part of
> the
> > + *  template data
> > + */
> > +int ima_eventevmsig_init(struct ima_event_data *event_data,
> > +			 struct ima_field_data *field_data)
> > +{
> > +	struct evm_ima_xattr_data *xattr_data = NULL;
> > +	int rc = 0;
> > +
> > +	if (!event_data->file)
> > +		return 0;
> > +
> > +	if (!(file_inode(event_data->file)->i_opflags & IOP_XATTR))
> > +		return 0;
> > +
> > +	rc = vfs_getxattr_alloc(file_dentry(event_data->file),
> XATTR_NAME_EVM,
> > +				(char **)&xattr_data, 0, GFP_NOFS);
> > +	if (rc <= 0) {
> > +		if (!rc || rc == -ENODATA)
> > +			return 0;
> > +
> > +		return rc;
> 
> We're including the EVM signature on a best effort basis to help with
> attestation.  Do we really care why it failed?   Are we going to act on
> it?

Hi Mimi

other template field functions have a similar behavior. They return
an error if an operation necessary to retrieve the data cannot be
performed. Should I always return 0?

Thanks

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

> Mimi
> 
> > +	}
> > +
> > +	if (xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG) {
> > +		kfree(xattr_data);
> > +		return 0;
> > +	}
> > +
> > +	rc = ima_write_template_field_data((char *)xattr_data, rc,
> DATA_FMT_HEX,
> > +					   field_data);
> > +	kfree(xattr_data);
> > +	return rc;
> > +}
>
Mimi Zohar Sept. 17, 2020, 3:55 p.m. UTC | #3
On Thu, 2020-09-17 at 15:05 +0000, Roberto Sassu wrote:
> > From: Mimi Zohar [mailto:zohar@linux.ibm.com]
> > Sent: Thursday, September 17, 2020 4:25 PM
> > Hi Roberto,
> > 
> > On Fri, 2020-09-04 at 11:26 +0200, Roberto Sassu wrote:
> > > With the patch to accept EVM portable signatures when the
> > > appraise_type=imasig requirement is specified in the policy, appraisal can
> > > be successfully done even if the file does not have an IMA signature.
> > >
> > > However, remote attestation would not see that a different signature
> > type
> > > was used, as only IMA signatures can be included in the measurement list.
> > > This patch solves the issue by introducing the new template field 'evmsig'
> > > to show EVM portable signatures and by including its value in the existing
> > > field 'sig' if the IMA signature is not found.
> > >
> > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > > Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
> > 
> > Thank you!   Just a minor comment below.
> > 
> > <snip>
> > 
> > > diff --git a/security/integrity/ima/ima_template_lib.c
> > b/security/integrity/ima/ima_template_lib.c
> > > index c022ee9e2a4e..2c596c2a89cc 100644
> > > --- a/security/integrity/ima/ima_template_lib.c
> > > +++ b/security/integrity/ima/ima_template_lib.c
> > >
> > > @@ -438,7 +439,7 @@ int ima_eventsig_init(struct ima_event_data
> > *event_data,
> > >  	struct evm_ima_xattr_data *xattr_value = event_data->xattr_value;
> > >
> > >  	if ((!xattr_value) || (xattr_value->type !=
> > EVM_IMA_XATTR_DIGSIG))
> > > -		return 0;
> > > +		return ima_eventevmsig_init(event_data, field_data);
> > >
> > >  	return ima_write_template_field_data(xattr_value, event_data-
> > >xattr_len,
> > >  					     DATA_FMT_HEX, field_data);
> > > @@ -484,3 +485,39 @@ int ima_eventmodsig_init(struct ima_event_data
> > *event_data,
> > >  	return ima_write_template_field_data(data, data_len,
> > DATA_FMT_HEX,
> > >  					     field_data);
> > >  }
> > > +
> > > +/*
> > > + *  ima_eventevmsig_init - include the EVM portable signature as part of
> > the
> > > + *  template data
> > > + */
> > > +int ima_eventevmsig_init(struct ima_event_data *event_data,
> > > +			 struct ima_field_data *field_data)
> > > +{
> > > +	struct evm_ima_xattr_data *xattr_data = NULL;
> > > +	int rc = 0;
> > > +
> > > +	if (!event_data->file)
> > > +		return 0;
> > > +
> > > +	if (!(file_inode(event_data->file)->i_opflags & IOP_XATTR))
> > > +		return 0;
> > > +
> > > +	rc = vfs_getxattr_alloc(file_dentry(event_data->file),
> > XATTR_NAME_EVM,
> > > +				(char **)&xattr_data, 0, GFP_NOFS);
> > > +	if (rc <= 0) {
> > > +		if (!rc || rc == -ENODATA)
> > > +			return 0;
> > > +
> > > +		return rc;
> > 
> > We're including the EVM signature on a best effort basis to help with
> > attestation.  Do we really care why it failed?   Are we going to act on
> > it?
> 
> Hi Mimi
> 
> other template field functions have a similar behavior. They return
> an error if an operation necessary to retrieve the data cannot be
> performed. Should I always return 0?

The EVM signature case is more similar to the IMA signature case, than
to other fields.  In the signature cases, if the signature exists, it
is included.   My suggestion is based on the difference in how the
vfs_getxattr_alloc() results are handled.

thanks,

Mimi
diff mbox series

Patch

diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst
index c5a8432972ef..9f3e86ab028a 100644
--- a/Documentation/security/IMA-templates.rst
+++ b/Documentation/security/IMA-templates.rst
@@ -70,9 +70,11 @@  descriptors by adding their identifier to the format string
    prefix is shown only if the hash algorithm is not SHA1 or MD5);
  - 'd-modsig': the digest of the event without the appended modsig;
  - 'n-ng': the name of the event, without size limitations;
- - 'sig': the file signature;
+ - 'sig': the file signature, or the EVM portable signature if the file
+   signature is not found;
  - 'modsig' the appended file signature;
  - 'buf': the buffer data that was used to generate the hash without size limitations;
+ - 'evmsig': the EVM portable signature;
 
 
 Below, there is the list of defined template descriptors:
diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
index 1e89e2d3851f..02afc4116606 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c
@@ -45,6 +45,8 @@  static const struct ima_template_field supported_fields[] = {
 	 .field_show = ima_show_template_digest_ng},
 	{.field_id = "modsig", .field_init = ima_eventmodsig_init,
 	 .field_show = ima_show_template_sig},
+	{.field_id = "evmsig", .field_init = ima_eventevmsig_init,
+	 .field_show = ima_show_template_sig},
 };
 
 /*
diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index c022ee9e2a4e..2c596c2a89cc 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c
@@ -10,6 +10,7 @@ 
  */
 
 #include "ima_template_lib.h"
+#include <linux/xattr.h>
 
 static bool ima_template_hash_algo_allowed(u8 algo)
 {
@@ -438,7 +439,7 @@  int ima_eventsig_init(struct ima_event_data *event_data,
 	struct evm_ima_xattr_data *xattr_value = event_data->xattr_value;
 
 	if ((!xattr_value) || (xattr_value->type != EVM_IMA_XATTR_DIGSIG))
-		return 0;
+		return ima_eventevmsig_init(event_data, field_data);
 
 	return ima_write_template_field_data(xattr_value, event_data->xattr_len,
 					     DATA_FMT_HEX, field_data);
@@ -484,3 +485,39 @@  int ima_eventmodsig_init(struct ima_event_data *event_data,
 	return ima_write_template_field_data(data, data_len, DATA_FMT_HEX,
 					     field_data);
 }
+
+/*
+ *  ima_eventevmsig_init - include the EVM portable signature as part of the
+ *  template data
+ */
+int ima_eventevmsig_init(struct ima_event_data *event_data,
+			 struct ima_field_data *field_data)
+{
+	struct evm_ima_xattr_data *xattr_data = NULL;
+	int rc = 0;
+
+	if (!event_data->file)
+		return 0;
+
+	if (!(file_inode(event_data->file)->i_opflags & IOP_XATTR))
+		return 0;
+
+	rc = vfs_getxattr_alloc(file_dentry(event_data->file), XATTR_NAME_EVM,
+				(char **)&xattr_data, 0, GFP_NOFS);
+	if (rc <= 0) {
+		if (!rc || rc == -ENODATA)
+			return 0;
+
+		return rc;
+	}
+
+	if (xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG) {
+		kfree(xattr_data);
+		return 0;
+	}
+
+	rc = ima_write_template_field_data((char *)xattr_data, rc, DATA_FMT_HEX,
+					   field_data);
+	kfree(xattr_data);
+	return rc;
+}
diff --git a/security/integrity/ima/ima_template_lib.h b/security/integrity/ima/ima_template_lib.h
index 6b3b880637a0..f4b2a2056d1d 100644
--- a/security/integrity/ima/ima_template_lib.h
+++ b/security/integrity/ima/ima_template_lib.h
@@ -46,4 +46,6 @@  int ima_eventbuf_init(struct ima_event_data *event_data,
 		      struct ima_field_data *field_data);
 int ima_eventmodsig_init(struct ima_event_data *event_data,
 			 struct ima_field_data *field_data);
+int ima_eventevmsig_init(struct ima_event_data *event_data,
+			 struct ima_field_data *field_data);
 #endif /* __LINUX_IMA_TEMPLATE_LIB_H */