On Fri, 2024-11-29 at 12:06 +0100, Mickaël Salaün wrote: > For reference, here is the base patch series: > https://lore.kernel.org/all/[email protected]/ > > CCing audit@ > > On Wed, Nov 27, 2024 at 04:02:34PM -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 integrity is optionally enforced by the interpreter. > > > > Update the audit messages to differentiate between kernel and userspace > > enforced integrity. > > I'm not sure to see the full picture. What is the difference between > execveat() calls and execveat() + AT_EXECVE_CHECK calls? Both are from > user space, the only difference is that the first can lead to a full > execution, but the intent is the same.
We do want the full execution in order to measure/appraise/audit both the direct file execution (e.g. ./script.sh) and the interpreter (e.g. #!/usr/bin/bash) specified. > > > > > Signed-off-by: Roberto Sassu <[email protected]> > > Signed-off-by: Mimi Zohar <[email protected]> > > --- > > security/integrity/ima/ima_appraise.c | 84 ++++++++++++++++++++------- > > security/integrity/ima/ima_main.c | 22 +++++++ > > 2 files changed, 86 insertions(+), 20 deletions(-) > > > > diff --git a/security/integrity/ima/ima_appraise.c > > b/security/integrity/ima/ima_appraise.c > > index 656c709b974f..b5f8e49cde9d 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> > > @@ -16,6 +17,7 @@ > > #include <linux/fsverity.h> > > #include <keys/system_keyring.h> > > #include <uapi/linux/fsverity.h> > > +#include <linux/securebits.h> > > > > #include "ima.h" > > > > @@ -276,7 +278,8 @@ static int calc_file_id_hash(enum evm_ima_xattr_type > > type, > > */ > > static int xattr_verify(enum ima_hooks func, struct ima_iint_cache *iint, > > struct evm_ima_xattr_data *xattr_value, int xattr_len, > > - enum integrity_status *status, const char **cause) > > + enum integrity_status *status, const char **cause, > > + bool is_check) > > { > > struct ima_max_digest_data hash; > > struct signature_v2_hdr *sig; > > @@ -292,9 +295,11 @@ static int xattr_verify(enum ima_hooks func, struct > > ima_iint_cache *iint, > > if (*status != INTEGRITY_PASS_IMMUTABLE) { > > if (iint->flags & IMA_DIGSIG_REQUIRED) { > > if (iint->flags & IMA_VERITY_REQUIRED) > > - *cause = "verity-signature-required"; > > + *cause = !is_check ? > > "verity-signature-required" : > > + > > "verity-signature-required(userspace)"; > > This looks simpler (same for all following checks): > is_check ? "verity-signature-required(userspace)" : > "verity-signature-required"; > > > else > > - *cause = "IMA-signature-required"; > > + *cause = !is_check ? > > "IMA-signature-required" : > > + > > "IMA-signature-required(userspace)"; > > *status = INTEGRITY_FAIL; > > break; > > } > > @@ -314,7 +319,8 @@ static int xattr_verify(enum ima_hooks func, struct > > ima_iint_cache *iint, > > else > > rc = -EINVAL; > > if (rc) { > > - *cause = "invalid-hash"; > > + *cause = !is_check ? "invalid-hash" : > > + "invalid-hash(userspace)"; > > *status = INTEGRITY_FAIL; > > break; > > } > > @@ -325,14 +331,16 @@ static int xattr_verify(enum ima_hooks func, struct > > ima_iint_cache *iint, > > > > mask = IMA_DIGSIG_REQUIRED | IMA_VERITY_REQUIRED; > > if ((iint->flags & mask) == mask) { > > - *cause = "verity-signature-required"; > > + *cause = !is_check ? "verity-signature-required" : > > + "verity-signature-required(userspace)"; > > *status = INTEGRITY_FAIL; > > break; > > } > > > > sig = (typeof(sig))xattr_value; > > if (sig->version >= 3) { > > - *cause = "invalid-signature-version"; > > + *cause = !is_check ? "invalid-signature-version" : > > + "invalid-signature-version(userspace)"; > > *status = INTEGRITY_FAIL; > > break; > > } > > @@ -353,7 +361,8 @@ static int xattr_verify(enum ima_hooks func, struct > > ima_iint_cache *iint, > > iint->ima_hash->digest, > > iint->ima_hash->length); > > if (rc) { > > - *cause = "invalid-signature"; > > + *cause = !is_check ? "invalid-signature" : > > + "invalid-signature(userspace)"; > > *status = INTEGRITY_FAIL; > > } else { > > *status = INTEGRITY_PASS; > > @@ -364,7 +373,8 @@ static int xattr_verify(enum ima_hooks func, struct > > ima_iint_cache *iint, > > > > if (iint->flags & IMA_DIGSIG_REQUIRED) { > > if (!(iint->flags & IMA_VERITY_REQUIRED)) { > > - *cause = "IMA-signature-required"; > > + *cause = !is_check ? "IMA-signature-required" : > > + "IMA-signature-required(userspace)"; > > *status = INTEGRITY_FAIL; > > break; > > } > > @@ -372,7 +382,8 @@ static int xattr_verify(enum ima_hooks func, struct > > ima_iint_cache *iint, > > > > sig = (typeof(sig))xattr_value; > > if (sig->version != 3) { > > - *cause = "invalid-signature-version"; > > + *cause = !is_check ? "invalid-signature-version" : > > + "invalid-signature-version(userspace)"; > > *status = INTEGRITY_FAIL; > > break; > > } > > @@ -382,7 +393,8 @@ static int xattr_verify(enum ima_hooks func, struct > > ima_iint_cache *iint, > > container_of(&hash.hdr, > > struct ima_digest_data, hdr)); > > if (rc) { > > - *cause = "sigv3-hashing-error"; > > + *cause = !is_check ? "sigv3-hashing-error" : > > + "sigv3-hashing-error(userspace)"; > > *status = INTEGRITY_FAIL; > > break; > > } > > @@ -392,7 +404,8 @@ static int xattr_verify(enum ima_hooks func, struct > > ima_iint_cache *iint, > > xattr_len, hash.digest, > > hash.hdr.length); > > if (rc) { > > - *cause = "invalid-verity-signature"; > > + *cause = !is_check ? "invalid-verity-signature" : > > + "invalid-verify-signature(userspace)"; > > *status = INTEGRITY_FAIL; > > } else { > > *status = INTEGRITY_PASS; > > @@ -401,7 +414,8 @@ static int xattr_verify(enum ima_hooks func, struct > > ima_iint_cache *iint, > > break; > > default: > > *status = INTEGRITY_UNKNOWN; > > - *cause = "unknown-ima-data"; > > + *cause = !is_check ? "unknown-ima-data" : > > + "unknown-ima-data(userspace)"; > > break; > > } > > > > @@ -469,6 +483,18 @@ int ima_check_blacklist(struct ima_iint_cache *iint, > > return rc; > > } > > > > +static int is_bprm_creds_for_exec(enum ima_hooks func, struct file *file) > > +{ > > + struct linux_binprm *bprm = NULL; > > + > > + if (func == BPRM_CHECK) { > > + bprm = container_of(&file, struct linux_binprm, file); > > + if (bprm->is_check) > > + return 1; > > + } > > + return 0; > > +} > > + > > /* > > * ima_appraise_measurement - appraise file measurement > > * > > @@ -489,11 +515,24 @@ int ima_appraise_measurement(enum ima_hooks func, > > struct ima_iint_cache *iint, > > enum integrity_status status = INTEGRITY_UNKNOWN; > > int rc = xattr_len; > > bool try_modsig = iint->flags & IMA_MODSIG_ALLOWED && modsig; > > + bool is_check = false; > > > > /* If not appraising a modsig, we need an xattr. */ > > 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 is left up to the discretion of the script interpreter > > + * (userspace). > > + * > > + * Since the SECBIT_EXEC_RESTRICT_FILE flag is just a hint as to > > + * userspace intentions, simply annotate the audit messages indicating > > + * a userspace based query. > > + */ > > + is_check = is_bprm_creds_for_exec(func, file); > > + > > /* If reading the xattr failed and there's no modsig, error out. */ > > if (rc <= 0 && !try_modsig) { > > if (rc && rc != -ENODATA) > > @@ -501,11 +540,14 @@ int ima_appraise_measurement(enum ima_hooks func, > > struct ima_iint_cache *iint, > > > > if (iint->flags & IMA_DIGSIG_REQUIRED) { > > if (iint->flags & IMA_VERITY_REQUIRED) > > - cause = "verity-signature-required"; > > + cause = !is_check ? "verity-signature-required" > > : > > + "verity-signature-required(userspace)"; > > else > > - cause = "IMA-signature-required"; > > + cause = !is_check ? "IMA-signature-required" : > > + "IMA-signature-required(userspace)"; > > } else { > > - cause = "missing-hash"; > > + cause = !is_check ? "missing-hash" : > > + "missing-hash(userspace)"; > > } > > > > status = INTEGRITY_NOLABEL; > > @@ -531,14 +573,15 @@ int ima_appraise_measurement(enum ima_hooks func, > > struct ima_iint_cache *iint, > > break; > > fallthrough; > > case INTEGRITY_NOLABEL: /* No security.evm xattr. */ > > - cause = "missing-HMAC"; > > + cause = !is_check ? "missing-HMAC" : "missing-HMAC(userspace)"; > > goto out; > > case INTEGRITY_FAIL_IMMUTABLE: > > set_bit(IMA_DIGSIG, &iint->atomic_flags); > > - cause = "invalid-fail-immutable"; > > + cause = !is_check ? "invalid-fail-immutable" : > > + "invalid-fail-immutable(userspace)"; > > goto out; > > case INTEGRITY_FAIL: /* Invalid HMAC/signature. */ > > - cause = "invalid-HMAC"; > > + cause = !is_check ? "invalid-HMAC" : "invalid-HMAC(userspace)"; > > goto out; > > default: > > WARN_ONCE(true, "Unexpected integrity status %d\n", status); > > @@ -546,7 +589,7 @@ int ima_appraise_measurement(enum ima_hooks func, > > struct ima_iint_cache *iint, > > > > if (xattr_value) > > rc = xattr_verify(func, iint, xattr_value, xattr_len, &status, > > - &cause); > > + &cause, is_check); > > > > /* > > * If we have a modsig and either no imasig or the imasig's key isn't > > @@ -568,7 +611,8 @@ int ima_appraise_measurement(enum ima_hooks func, > > struct ima_iint_cache *iint, > > ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) || > > (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) { > > status = INTEGRITY_FAIL; > > - cause = "unverifiable-signature"; > > + cause = !is_check ? "unverifiable-signature" : > > + "unverifiable-signature(userspace)"; > > integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename, > > op, cause, rc, 0); > > Instead of adding new causes, another option would be to add a new audit > record type (e.g. AUDIT_INTEGRITY_DATA_CHECK). This would help filter > these new kind of messages and I guess scale better. Thanks. This sounds like a better alternative. > > Another alternative would be to extend the audit message with a new > field (e.g. "check=1"), but that would not help for efficient filtering. > > > } else if (status != INTEGRITY_PASS) { > > diff --git a/security/integrity/ima/ima_main.c > > b/security/integrity/ima/ima_main.c > > index 06132cf47016..2b5d6bae77a4 100644 > > --- a/security/integrity/ima/ima_main.c > > +++ b/security/integrity/ima/ima_main.c > > @@ -554,6 +554,27 @@ static int ima_bprm_check(struct linux_binprm *bprm) > > MAY_EXEC, CREDS_CHECK); > > } > > > > +/** > > + * ima_bprm_creds_for_exec - based on policy, collect/store/appraise > > measurement. > > + * @bprm: contains the linux_binprm structure > > + * > > + * Based on the IMA policy and the execvat(2) AT_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) > > +{ > > + 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 +1198,7 @@ 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), > > Why not replace bprm_check_security with bprm_creds_for_exec > implementation altogether? To measure/appraise/audit the interpreter specified in the direct file (e.g. ./script.sh). > > > 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), > > -- > > 2.47.0 > > > > >
