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 <[email protected]> > Signed-off-by: Roberto Sassu <[email protected]> > Signed-off-by: Mimi Zohar <[email protected]> > --- > 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),
