[v2] ima: instantiate the bprm_creds_for_exec() hook

Commit Message

Mimi Zohar Dec. 4, 2024, 7:25 p.m. UTC

Like direct file execution (e.g. ./script.sh), indirect file execution
(e.g. sh script.sh) needs to be measured and appraised.  Instantiate
the new security_bprm_creds_for_exec() hook to measure and verify the
indirect file's integrity.  Unlike direct file execution, indirect file
execution is optionally enforced by the interpreter.

Differentiate kernel and userspace enforced integrity audit messages.

Co-developed-by: Roberto Sassu <[e-mail]>
Signed-off-by: Roberto Sassu <[e-mail]>
Signed-off-by: Mimi Zohar <[e-mail]>
---
Changelog v3:
- Mickael: add comment ima_bprm_creds_for_exec(), minor code cleanup,
  add Co-developed-by tag.

Changelog v2:
- Mickael: Use same audit messages with new audit message number
- Stefan Berger: Return boolean from is_bprm_creds_for_exec()

 include/uapi/linux/audit.h            |  1 +
 security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++++--
 security/integrity/ima/ima_main.c     | 29 +++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 2 deletions(-)

Comments

Mimi Zohar Dec. 4, 2024, 7:27 p.m. UTC | #1

This should have been patch v3.

Mimi

On Wed, 2024-12-04 at 14:25 -0500, Mimi Zohar wrote:
> Like direct file execution (e.g. ./script.sh), indirect file execution
> (e.g. sh script.sh) needs to be measured and appraised.  Instantiate
> the new security_bprm_creds_for_exec() hook to measure and verify the
> indirect file's integrity.  Unlike direct file execution, indirect file
> execution is optionally enforced by the interpreter.
> 
> Differentiate kernel and userspace enforced integrity audit messages.
> 
> Co-developed-by: Roberto Sassu <[e-mail]>
> Signed-off-by: Roberto Sassu <[e-mail]>
> Signed-off-by: Mimi Zohar <[e-mail]>
> ---
> Changelog v3:
> - Mickael: add comment ima_bprm_creds_for_exec(), minor code cleanup,
>   add Co-developed-by tag.
> 
> Changelog v2:
> - Mickael: Use same audit messages with new audit message number
> - Stefan Berger: Return boolean from is_bprm_creds_for_exec()
> 
>  include/uapi/linux/audit.h            |  1 +
>  security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++++--
>  security/integrity/ima/ima_main.c     | 29 +++++++++++++++++++++++++++
>  3 files changed, 55 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index 75e21a135483..826337905466 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -161,6 +161,7 @@
>  #define AUDIT_INTEGRITY_RULE	    1805 /* policy rule */
>  #define AUDIT_INTEGRITY_EVM_XATTR   1806 /* New EVM-covered xattr */
>  #define AUDIT_INTEGRITY_POLICY_RULE 1807 /* IMA policy rules */
> +#define AUDIT_INTEGRITY_DATA_CHECK  1808 /* Userspace enforced data integrity */
>  
>  #define AUDIT_KERNEL		2000	/* Asynchronous audit record. NOT A REQUEST. */
>  
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 656c709b974f..fc0d1f3cceca 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -8,6 +8,7 @@
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/file.h>
> +#include <linux/binfmts.h>
>  #include <linux/fs.h>
>  #include <linux/xattr.h>
>  #include <linux/magic.h>
> @@ -469,6 +470,17 @@ int ima_check_blacklist(struct ima_iint_cache *iint,
>  	return rc;
>  }
>  
> +static bool is_bprm_creds_for_exec(enum ima_hooks func, struct file *file)
> +{
> +	struct linux_binprm *bprm;
> +
> +	if (func == BPRM_CHECK) {
> +		bprm = container_of(&file, struct linux_binprm, file);
> +		return bprm->is_check;
> +	}
> +	return false;
> +}
> +
>  /*
>   * ima_appraise_measurement - appraise file measurement
>   *
> @@ -483,6 +495,7 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
>  			     int xattr_len, const struct modsig *modsig)
>  {
>  	static const char op[] = "appraise_data";
> +	int audit_msgno = AUDIT_INTEGRITY_DATA;
>  	const char *cause = "unknown";
>  	struct dentry *dentry = file_dentry(file);
>  	struct inode *inode = d_backing_inode(dentry);
> @@ -494,6 +507,16 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
>  	if (!(inode->i_opflags & IOP_XATTR) && !try_modsig)
>  		return INTEGRITY_UNKNOWN;
>  
> +	/*
> +	 * Unlike any of the other LSM hooks where the kernel enforces file
> +	 * integrity, enforcing file integrity for the bprm_creds_for_exec()
> +	 * LSM hook with the AT_EXECVE_CHECK flag is left up to the discretion
> +	 * of the script interpreter(userspace). Differentiate kernel and
> +	 * userspace enforced integrity audit messages.
> +	 */
> +	if (is_bprm_creds_for_exec(func, file))
> +		audit_msgno = AUDIT_INTEGRITY_DATA_CHECK;
> +
>  	/* If reading the xattr failed and there's no modsig, error out. */
>  	if (rc <= 0 && !try_modsig) {
>  		if (rc && rc != -ENODATA)
> @@ -569,7 +592,7 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
>  	     (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
>  		status = INTEGRITY_FAIL;
>  		cause = "unverifiable-signature";
> -		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
> +		integrity_audit_msg(audit_msgno, inode, filename,
>  				    op, cause, rc, 0);
>  	} else if (status != INTEGRITY_PASS) {
>  		/* Fix mode, but don't replace file signatures. */
> @@ -589,7 +612,7 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
>  			status = INTEGRITY_PASS;
>  		}
>  
> -		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
> +		integrity_audit_msg(audit_msgno, inode, filename,
>  				    op, cause, rc, 0);
>  	} else {
>  		ima_cache_flags(iint, func);
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 06132cf47016..5d4ac8aa2f1f 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -554,6 +554,34 @@ static int ima_bprm_check(struct linux_binprm *bprm)
>  				   MAY_EXEC, CREDS_CHECK);
>  }
>  
> +/**
> + * ima_bprm_creds_for_exec - collect/store/appraise measurement.
> + * @bprm: contains the linux_binprm structure
> + *
> + * Based on the IMA policy and the execvat(2) AT_EXECVE_CHECK flag, measure
> + * and appraise the integrity of a file to be executed by script interpreters.
> + * Unlike any of the other LSM hooks where the kernel enforces file integrity,
> + * enforcing file integrity is left up to the discretion of the script
> + * interpreter (userspace).
> + *
> + * On success return 0.  On integrity appraisal error, assuming the file
> + * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
> + */
> +static int ima_bprm_creds_for_exec(struct linux_binprm *bprm)
> +{
> +	/*
> +	 * As security_bprm_check() is called multiple times, both
> +	 * the script and the shebang interpreter are measured, appraised,
> +	 * and audited. Limit usage of this LSM hook to just measuring,
> +	 * appraising, and auditing the indirect script execution
> +	 * (e.g. ./sh example.sh).
> +	 */
> +	if (!bprm->is_check)
> +		return 0;
> +
> +	return ima_bprm_check(bprm);
> +}
> +
>  /**
>   * ima_file_check - based on policy, collect/store measurement.
>   * @file: pointer to the file to be measured
> @@ -1177,6 +1205,7 @@ static int __init init_ima(void)
>  
>  static struct security_hook_list ima_hooks[] __ro_after_init = {
>  	LSM_HOOK_INIT(bprm_check_security, ima_bprm_check),
> +	LSM_HOOK_INIT(bprm_creds_for_exec, ima_bprm_creds_for_exec),
>  	LSM_HOOK_INIT(file_post_open, ima_file_check),
>  	LSM_HOOK_INIT(inode_post_create_tmpfile, ima_post_create_tmpfile),
>  	LSM_HOOK_INIT(file_release, ima_file_free),

Paul Moore Dec. 6, 2024, 12:30 a.m. UTC | #2

On Dec  4, 2024 Mimi Zohar <[e-mail]> wrote:
> 
> Like direct file execution (e.g. ./script.sh), indirect file execution
> (e.g. sh script.sh) needs to be measured and appraised.  Instantiate
> the new security_bprm_creds_for_exec() hook to measure and verify the
> indirect file's integrity.  Unlike direct file execution, indirect file
> execution is optionally enforced by the interpreter.
> 
> Differentiate kernel and userspace enforced integrity audit messages.
> 
> Co-developed-by: Roberto Sassu <[e-mail]>
> Signed-off-by: Roberto Sassu <[e-mail]>
> Signed-off-by: Mimi Zohar <[e-mail]>
> ---
> Changelog v3:
> - Mickael: add comment ima_bprm_creds_for_exec(), minor code cleanup,
>   add Co-developed-by tag.
> 
> Changelog v2:
> - Mickael: Use same audit messages with new audit message number
> - Stefan Berger: Return boolean from is_bprm_creds_for_exec()
> 
>  include/uapi/linux/audit.h            |  1 +
>  security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++++--
>  security/integrity/ima/ima_main.c     | 29 +++++++++++++++++++++++++++
>  3 files changed, 55 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index 75e21a135483..826337905466 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -161,6 +161,7 @@
>  #define AUDIT_INTEGRITY_RULE	    1805 /* policy rule */
>  #define AUDIT_INTEGRITY_EVM_XATTR   1806 /* New EVM-covered xattr */
>  #define AUDIT_INTEGRITY_POLICY_RULE 1807 /* IMA policy rules */
> +#define AUDIT_INTEGRITY_DATA_CHECK  1808 /* Userspace enforced data integrity */

I worry that "DATA_CHECK" is a bit vague, should we change the name so
that there is some hint of either userspace enforcement or
AT_EXECVE_CHECK?

What about AUDIT_INTEGRITY_DATA_USER?

--
paul-moore.com

Mimi Zohar Dec. 6, 2024, 3:10 a.m. UTC | #3

On Thu, 2024-12-05 at 19:30 -0500, Paul Moore wrote:
> On Dec  4, 2024 Mimi Zohar <[e-mail]> wrote:
> > 
> > Like direct file execution (e.g. ./script.sh), indirect file execution
> > (e.g. sh script.sh) needs to be measured and appraised.  Instantiate
> > the new security_bprm_creds_for_exec() hook to measure and verify the
> > indirect file's integrity.  Unlike direct file execution, indirect file
> > execution is optionally enforced by the interpreter.
> > 
> > Differentiate kernel and userspace enforced integrity audit messages.
> > 
> > Co-developed-by: Roberto Sassu <[e-mail]>
> > Signed-off-by: Roberto Sassu <[e-mail]>
> > Signed-off-by: Mimi Zohar <[e-mail]>
> > ---
> > Changelog v3:
> > - Mickael: add comment ima_bprm_creds_for_exec(), minor code cleanup,
> >   add Co-developed-by tag.
> > 
> > Changelog v2:
> > - Mickael: Use same audit messages with new audit message number
> > - Stefan Berger: Return boolean from is_bprm_creds_for_exec()
> > 
> >  include/uapi/linux/audit.h            |  1 +
> >  security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++++--
> >  security/integrity/ima/ima_main.c     | 29 +++++++++++++++++++++++++++
> >  3 files changed, 55 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > index 75e21a135483..826337905466 100644
> > --- a/include/uapi/linux/audit.h
> > +++ b/include/uapi/linux/audit.h
> > @@ -161,6 +161,7 @@
> >  #define AUDIT_INTEGRITY_RULE	    1805 /* policy rule */
> >  #define AUDIT_INTEGRITY_EVM_XATTR   1806 /* New EVM-covered xattr */
> >  #define AUDIT_INTEGRITY_POLICY_RULE 1807 /* IMA policy rules */
> > +#define AUDIT_INTEGRITY_DATA_CHECK  1808 /* Userspace enforced data integrity */
> 
> I worry that "DATA_CHECK" is a bit vague, should we change the name so
> that there is some hint of either userspace enforcement or
> AT_EXECVE_CHECK?
> 
> What about AUDIT_INTEGRITY_DATA_USER?

The emphasis should be on userspace - AUDIT_INTEGRITY_USERSPACE.

Mimi

Mickaël Salaün Dec. 10, 2024, 4:34 p.m. UTC | #4

On Thu, Dec 05, 2024 at 10:10:36PM -0500, Mimi Zohar wrote:
> On Thu, 2024-12-05 at 19:30 -0500, Paul Moore wrote:
> > On Dec  4, 2024 Mimi Zohar <[e-mail]> wrote:
> > > 
> > > Like direct file execution (e.g. ./script.sh), indirect file execution
> > > (e.g. sh script.sh) needs to be measured and appraised.  Instantiate
> > > the new security_bprm_creds_for_exec() hook to measure and verify the
> > > indirect file's integrity.  Unlike direct file execution, indirect file
> > > execution is optionally enforced by the interpreter.
> > > 
> > > Differentiate kernel and userspace enforced integrity audit messages.
> > > 
> > > Co-developed-by: Roberto Sassu <[e-mail]>
> > > Signed-off-by: Roberto Sassu <[e-mail]>
> > > Signed-off-by: Mimi Zohar <[e-mail]>
> > > ---
> > > Changelog v3:
> > > - Mickael: add comment ima_bprm_creds_for_exec(), minor code cleanup,
> > >   add Co-developed-by tag.
> > > 
> > > Changelog v2:
> > > - Mickael: Use same audit messages with new audit message number
> > > - Stefan Berger: Return boolean from is_bprm_creds_for_exec()
> > > 
> > >  include/uapi/linux/audit.h            |  1 +
> > >  security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++++--
> > >  security/integrity/ima/ima_main.c     | 29 +++++++++++++++++++++++++++
> > >  3 files changed, 55 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > > index 75e21a135483..826337905466 100644
> > > --- a/include/uapi/linux/audit.h
> > > +++ b/include/uapi/linux/audit.h
> > > @@ -161,6 +161,7 @@
> > >  #define AUDIT_INTEGRITY_RULE	    1805 /* policy rule */
> > >  #define AUDIT_INTEGRITY_EVM_XATTR   1806 /* New EVM-covered xattr */
> > >  #define AUDIT_INTEGRITY_POLICY_RULE 1807 /* IMA policy rules */
> > > +#define AUDIT_INTEGRITY_DATA_CHECK  1808 /* Userspace enforced data integrity */
> > 
> > I worry that "DATA_CHECK" is a bit vague, should we change the name so
> > that there is some hint of either userspace enforcement or
> > AT_EXECVE_CHECK?
> > 
> > What about AUDIT_INTEGRITY_DATA_USER?
> 
> The emphasis should be on userspace - AUDIT_INTEGRITY_USERSPACE.

Looks good, I'll send a new patch series with this change, following
https://lore.kernel.org/all/[e-mail]/

Mimi Zohar Dec. 10, 2024, 4:47 p.m. UTC | #5

On Tue, 2024-12-10 at 17:34 +0100, Mickaël Salaün wrote:
> > > > +++ b/include/uapi/linux/audit.h
> > > > @@ -161,6 +161,7 @@
> > > >   #define AUDIT_INTEGRITY_RULE	    1805 /* policy rule */
> > > >   #define AUDIT_INTEGRITY_EVM_XATTR   1806 /* New EVM-covered xattr */
> > > >   #define AUDIT_INTEGRITY_POLICY_RULE 1807 /* IMA policy rules */
> > > > +#define AUDIT_INTEGRITY_DATA_CHECK  1808 /* Userspace enforced data integrity */
> > > 
> > > I worry that "DATA_CHECK" is a bit vague, should we change the name so
> > > that there is some hint of either userspace enforcement or
> > > AT_EXECVE_CHECK?
> > > 
> > > What about AUDIT_INTEGRITY_DATA_USER?
> > 
> > The emphasis should be on userspace - AUDIT_INTEGRITY_USERSPACE.
> 
> Looks good, I'll send a new patch series with this change, following
> https://lore.kernel.org/all/[e-mail]/

Sound good!  Thank you.

Mimi

Patch

diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 75e21a135483..826337905466 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -161,6 +161,7 @@ 
 #define AUDIT_INTEGRITY_RULE	    1805 /* policy rule */
 #define AUDIT_INTEGRITY_EVM_XATTR   1806 /* New EVM-covered xattr */
 #define AUDIT_INTEGRITY_POLICY_RULE 1807 /* IMA policy rules */
+#define AUDIT_INTEGRITY_DATA_CHECK  1808 /* Userspace enforced data integrity */
 
 #define AUDIT_KERNEL		2000	/* Asynchronous audit record. NOT A REQUEST. */
 
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 656c709b974f..fc0d1f3cceca 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -8,6 +8,7 @@ 
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/file.h>
+#include <linux/binfmts.h>
 #include <linux/fs.h>
 #include <linux/xattr.h>
 #include <linux/magic.h>
@@ -469,6 +470,17 @@  int ima_check_blacklist(struct ima_iint_cache *iint,
 	return rc;
 }
 
+static bool is_bprm_creds_for_exec(enum ima_hooks func, struct file *file)
+{
+	struct linux_binprm *bprm;
+
+	if (func == BPRM_CHECK) {
+		bprm = container_of(&file, struct linux_binprm, file);
+		return bprm->is_check;
+	}
+	return false;
+}
+
 /*
  * ima_appraise_measurement - appraise file measurement
  *
@@ -483,6 +495,7 @@  int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
 			     int xattr_len, const struct modsig *modsig)
 {
 	static const char op[] = "appraise_data";
+	int audit_msgno = AUDIT_INTEGRITY_DATA;
 	const char *cause = "unknown";
 	struct dentry *dentry = file_dentry(file);
 	struct inode *inode = d_backing_inode(dentry);
@@ -494,6 +507,16 @@  int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
 	if (!(inode->i_opflags & IOP_XATTR) && !try_modsig)
 		return INTEGRITY_UNKNOWN;
 
+	/*
+	 * Unlike any of the other LSM hooks where the kernel enforces file
+	 * integrity, enforcing file integrity for the bprm_creds_for_exec()
+	 * LSM hook with the AT_EXECVE_CHECK flag is left up to the discretion
+	 * of the script interpreter(userspace). Differentiate kernel and
+	 * userspace enforced integrity audit messages.
+	 */
+	if (is_bprm_creds_for_exec(func, file))
+		audit_msgno = AUDIT_INTEGRITY_DATA_CHECK;
+
 	/* If reading the xattr failed and there's no modsig, error out. */
 	if (rc <= 0 && !try_modsig) {
 		if (rc && rc != -ENODATA)
@@ -569,7 +592,7 @@  int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
 	     (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
 		status = INTEGRITY_FAIL;
 		cause = "unverifiable-signature";
-		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
+		integrity_audit_msg(audit_msgno, inode, filename,
 				    op, cause, rc, 0);
 	} else if (status != INTEGRITY_PASS) {
 		/* Fix mode, but don't replace file signatures. */
@@ -589,7 +612,7 @@  int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
 			status = INTEGRITY_PASS;
 		}
 
-		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
+		integrity_audit_msg(audit_msgno, inode, filename,
 				    op, cause, rc, 0);
 	} else {
 		ima_cache_flags(iint, func);
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 06132cf47016..5d4ac8aa2f1f 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -554,6 +554,34 @@  static int ima_bprm_check(struct linux_binprm *bprm)
 				   MAY_EXEC, CREDS_CHECK);
 }
 
+/**
+ * ima_bprm_creds_for_exec - collect/store/appraise measurement.
+ * @bprm: contains the linux_binprm structure
+ *
+ * Based on the IMA policy and the execvat(2) AT_EXECVE_CHECK flag, measure
+ * and appraise the integrity of a file to be executed by script interpreters.
+ * Unlike any of the other LSM hooks where the kernel enforces file integrity,
+ * enforcing file integrity is left up to the discretion of the script
+ * interpreter (userspace).
+ *
+ * On success return 0.  On integrity appraisal error, assuming the file
+ * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
+ */
+static int ima_bprm_creds_for_exec(struct linux_binprm *bprm)
+{
+	/*
+	 * As security_bprm_check() is called multiple times, both
+	 * the script and the shebang interpreter are measured, appraised,
+	 * and audited. Limit usage of this LSM hook to just measuring,
+	 * appraising, and auditing the indirect script execution
+	 * (e.g. ./sh example.sh).
+	 */
+	if (!bprm->is_check)
+		return 0;
+
+	return ima_bprm_check(bprm);
+}
+
 /**
  * ima_file_check - based on policy, collect/store measurement.
  * @file: pointer to the file to be measured
@@ -1177,6 +1205,7 @@  static int __init init_ima(void)
 
 static struct security_hook_list ima_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(bprm_check_security, ima_bprm_check),
+	LSM_HOOK_INIT(bprm_creds_for_exec, ima_bprm_creds_for_exec),
 	LSM_HOOK_INIT(file_post_open, ima_file_check),
 	LSM_HOOK_INIT(inode_post_create_tmpfile, ima_post_create_tmpfile),
 	LSM_HOOK_INIT(file_release, ima_file_free),