From: Thiago Jung Bauermann Subject: [PATCH v5 17/18] ima: Implement support for module-style appended signatures Date: Tue, 17 Oct 2017 22:53:30 -0200 Message-ID: <20171018005331.2688-18-bauerman@linux.vnet.ibm.com> References: <20171018005331.2688-1-bauerman@linux.vnet.ibm.com> Cc: linux-security-module@vger.kernel.org, keyrings@vger.kernel.org, linux-crypto@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Mimi Zohar , Dmitry Kasatkin , James Morris , "Serge E. Hallyn" , David Howells , David Woodhouse , Jessica Yu , Rusty Russell , Herbert Xu , "David S. Miller" , "AKASHI, Takahiro" , Thiago Jung Bauermann To: linux-integrity@vger.kernel.org Return-path: In-Reply-To: <20171018005331.2688-1-bauerman@linux.vnet.ibm.com> Sender: owner-linux-security-module@vger.kernel.org List-Id: linux-crypto.vger.kernel.org This patch actually implements the appraise_type=modsig option, allowing IMA to read and verify modsig signatures Signed-off-by: Thiago Jung Bauermann --- security/integrity/ima/ima.h | 17 +++-- security/integrity/ima/ima_appraise.c | 119 ++++++++++++++++++++++++++++++++-- security/integrity/ima/ima_main.c | 7 +- 3 files changed, 128 insertions(+), 15 deletions(-) diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index eb58af06566f..b082138461b3 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -157,7 +157,8 @@ void ima_init_template_list(void); static inline bool is_ima_sig(const struct evm_ima_xattr_data *xattr_value) { - return xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG; + return xattr_value && (xattr_value->type == EVM_IMA_XATTR_DIGSIG || + xattr_value->type == IMA_MODSIG); } /* @@ -243,9 +244,10 @@ int ima_policy_show(struct seq_file *m, void *v); #ifdef CONFIG_IMA_APPRAISE int ima_appraise_measurement(enum ima_hooks func, struct integrity_iint_cache *iint, - struct file *file, const unsigned char *filename, - struct evm_ima_xattr_data *xattr_value, - int xattr_len, int opened); + struct file *file, const void *buf, loff_t size, + const unsigned char *filename, + struct evm_ima_xattr_data **xattr_value, + int *xattr_len, int opened); int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func); void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file); enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint, @@ -270,10 +272,11 @@ void ima_free_xattr_data(struct evm_ima_xattr_data *hdr); #else static inline int ima_appraise_measurement(enum ima_hooks func, struct integrity_iint_cache *iint, - struct file *file, + struct file *file, const void *buf, + loff_t size, const unsigned char *filename, - struct evm_ima_xattr_data *xattr_value, - int xattr_len, int opened) + struct evm_ima_xattr_data **xattr_value, + int *xattr_len, int opened) { return INTEGRITY_UNKNOWN; } diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index 58e147049e98..108690741c1a 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -190,6 +190,45 @@ int ima_read_xattr(struct dentry *dentry, return ret; } +static int appraise_modsig(struct integrity_iint_cache *iint, + struct evm_ima_xattr_data *xattr_value, + int xattr_len) +{ + enum hash_algo algo; + const void *digest; + void *buf; + int rc, len; + u8 dig_len; + + rc = ima_modsig_verify(INTEGRITY_KEYRING_IMA, xattr_value); + if (rc) + return rc; + + /* + * The signature is good. Now let's put the sig hash + * into the iint cache so that it gets stored in the + * measurement list. + */ + + rc = ima_get_modsig_hash(xattr_value, &algo, &digest, &dig_len); + if (rc) + return rc; + + len = sizeof(iint->ima_hash) + dig_len; + buf = krealloc(iint->ima_hash, len, GFP_NOFS); + if (!buf) + return -ENOMEM; + + iint->ima_hash = buf; + iint->flags |= IMA_DIGSIG; + iint->ima_hash->algo = algo; + iint->ima_hash->length = dig_len; + + memcpy(iint->ima_hash->digest, digest, dig_len); + + return 0; +} + /* * ima_appraise_measurement - appraise file measurement * @@ -200,18 +239,28 @@ int ima_read_xattr(struct dentry *dentry, */ int ima_appraise_measurement(enum ima_hooks func, struct integrity_iint_cache *iint, - struct file *file, const unsigned char *filename, - struct evm_ima_xattr_data *xattr_value, - int xattr_len, int opened) + struct file *file, const void *buf, loff_t size, + const unsigned char *filename, + struct evm_ima_xattr_data **xattr_value_, + int *xattr_len_, int opened) { static const char op[] = "appraise_data"; const char *cause = "unknown"; struct dentry *dentry = file_dentry(file); struct inode *inode = d_backing_inode(dentry); enum integrity_status status = INTEGRITY_UNKNOWN; - int rc = xattr_len, hash_start = 0; + struct evm_ima_xattr_data *xattr_value = *xattr_value_; + int xattr_len = *xattr_len_, rc = xattr_len, hash_start = 0; + bool appraising_modsig = false; + + if (iint->flags & IMA_MODSIG_ALLOWED && + !ima_read_modsig(func, buf, size, &xattr_value, &xattr_len)) { + appraising_modsig = true; + rc = xattr_len; + } - if (!(inode->i_opflags & IOP_XATTR)) + /* If not appraising a modsig, we need an xattr. */ + if (!appraising_modsig && !(inode->i_opflags & IOP_XATTR)) return INTEGRITY_UNKNOWN; if (rc <= 0) { @@ -235,6 +284,9 @@ int ima_appraise_measurement(enum ima_hooks func, case INTEGRITY_UNKNOWN: break; case INTEGRITY_NOXATTRS: /* No EVM protected xattrs. */ + /* It's fine not to have xattrs when using a modsig. */ + if (appraising_modsig) + break; case INTEGRITY_NOLABEL: /* No security.evm xattr. */ cause = "missing-HMAC"; goto out; @@ -242,6 +294,8 @@ int ima_appraise_measurement(enum ima_hooks func, cause = "invalid-HMAC"; goto out; } + + retry: switch (xattr_value->type) { case IMA_XATTR_DIGEST_NG: /* first byte contains algorithm id */ @@ -285,6 +339,61 @@ int ima_appraise_measurement(enum ima_hooks func, status = INTEGRITY_PASS; } break; + case IMA_MODSIG: + /* + * To avoid being tricked into an infinite loop, we don't allow + * a modsig stored in the xattr. + */ + if (!appraising_modsig) { + status = INTEGRITY_UNKNOWN; + cause = "unknown-ima-data"; + break; + } + + rc = appraise_modsig(iint, xattr_value, xattr_len); + if (!rc) { + kfree(*xattr_value_); + *xattr_value_ = xattr_value; + *xattr_len_ = xattr_len; + + status = INTEGRITY_PASS; + break; + } + + ima_free_xattr_data(xattr_value); + + /* + * The appended signature failed verification. If there's a + * signature in the extended attribute, let's fall back to it. + */ + if (inode->i_opflags & IOP_XATTR && *xattr_len_ != 0 && + *xattr_len_ != -ENODATA) { + const char *modsig_cause = rc == -EOPNOTSUPP ? + "unknown" : "invalid-signature"; + + /* First, log that the modsig verification failed. */ + integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, + filename, op, modsig_cause, rc, 0); + + xattr_len = rc = *xattr_len_; + xattr_value = *xattr_value_; + appraising_modsig = false; + + if (rc > 0) + /* Process xattr contents. */ + goto retry; + + /* Unexpected error reading xattr. */ + status = INTEGRITY_UNKNOWN; + } else { + if (rc == -EOPNOTSUPP) + status = INTEGRITY_UNKNOWN; + else { + cause = "invalid-signature"; + status = INTEGRITY_FAIL; + } + } + break; default: status = INTEGRITY_UNKNOWN; cause = "unknown-ima-data"; diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index 8e96450e27f5..6a2d960fbd92 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -243,8 +243,9 @@ static int process_measurement(struct file *file, char *buf, loff_t size, pathname = ima_d_path(&file->f_path, &pathbuf, filename); if (rc == 0 && (action & IMA_APPRAISE_SUBMASK)) - rc = ima_appraise_measurement(func, iint, file, pathname, - xattr_value, xattr_len, opened); + rc = ima_appraise_measurement(func, iint, file, buf, size, + pathname, &xattr_value, + &xattr_len, opened); if (action & IMA_MEASURE) ima_store_measurement(iint, file, pathname, xattr_value, xattr_len, pcr); @@ -255,7 +256,7 @@ static int process_measurement(struct file *file, char *buf, loff_t size, if ((mask & MAY_WRITE) && (iint->flags & IMA_DIGSIG) && !(iint->flags & IMA_NEW_FILE)) rc = -EACCES; - kfree(xattr_value); + ima_free_xattr_data(xattr_value); out_free: if (pathbuf) __putname(pathbuf);