ima: Access decompressed kernel module to verify appended signature

Currently, when in-kernel module decompression (CONFIG_MODULE_DECOMPRESS)
is enabled, IMA has no way to verify the appended module signature as it
can't decompress the module.

Define a new kernel_read_file_id enumerate READING_MODULE_COMPRESSED so
IMA can calculate the compressed kernel module data hash on
READING_MODULE_COMPRESSED and defer appraising/measuring it until on
READING_MODULE when the module has been decompressed.

Before enabling in-kernel module decompression, a kernel module in
initramfs can still be loaded with ima_policy=secure_boot. So adjust the
kernel module rule in secure_boot policy to allow either an IMA
signature OR an appended signature i.e. to use
"appraise func=MODULE_CHECK appraise_type=imasig|modsig".

Reported-by: Karel Srot <ksrot@redhat.com>
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
Suggested-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Coiby Xu <coxu@redhat.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

1 files changed, 16 insertions, 8 deletions

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index ebaebccfbe9a..edd0fd3d77a0 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -235,7 +235,8 @@ static void ima_file_free(struct file *file)
 
 static int process_measurement(struct file *file, const struct cred *cred,
 			       struct lsm_prop *prop, char *buf, loff_t size,
-			       int mask, enum ima_hooks func)
+			       int mask, enum ima_hooks func,
+			       enum kernel_read_file_id read_id)
 {
 	struct inode *real_inode, *inode = file_inode(file);
 	struct ima_iint_cache *iint = NULL;
@@ -406,6 +407,12 @@ static int process_measurement(struct file *file, const struct cred *cred,
 	if (rc != 0 && rc != -EBADF && rc != -EINVAL)
 		goto out_locked;
 
+	/* Defer measuring/appraising kernel modules to READING_MODULE */
+	if (read_id == READING_MODULE_COMPRESSED) {
+		must_appraise = 0;
+		goto out_locked;
+	}
+
 	if (!pathbuf)	/* ima_rdwr_violation possibly pre-fetched */
 		pathname = ima_d_path(&file->f_path, &pathbuf, filename);
 
@@ -486,14 +493,14 @@ static int ima_file_mmap(struct file *file, unsigned long reqprot,
 
 	if (reqprot & PROT_EXEC) {
 		ret = process_measurement(file, current_cred(), &prop, NULL,
-					  0, MAY_EXEC, MMAP_CHECK_REQPROT);
+					  0, MAY_EXEC, MMAP_CHECK_REQPROT, 0);
 		if (ret)
 			return ret;
 	}
 
 	if (prot & PROT_EXEC)
 		return process_measurement(file, current_cred(), &prop, NULL,
-					   0, MAY_EXEC, MMAP_CHECK);
+					   0, MAY_EXEC, MMAP_CHECK, 0);
 
 	return 0;
 }
@@ -577,7 +584,7 @@ static int ima_bprm_check(struct linux_binprm *bprm)
 
 	security_current_getlsmprop_subj(&prop);
 	return process_measurement(bprm->file, current_cred(),
-				   &prop, NULL, 0, MAY_EXEC, BPRM_CHECK);
+				   &prop, NULL, 0, MAY_EXEC, BPRM_CHECK, 0);
 }
 
 /**
@@ -607,7 +614,7 @@ static int ima_creds_check(struct linux_binprm *bprm, const struct file *file)
 
 	security_current_getlsmprop_subj(&prop);
 	return process_measurement((struct file *)file, bprm->cred, &prop, NULL,
-				   0, MAY_EXEC, CREDS_CHECK);
+				   0, MAY_EXEC, CREDS_CHECK, 0);
 }
 
 /**
@@ -655,7 +662,7 @@ static int ima_file_check(struct file *file, int mask)
 	security_current_getlsmprop_subj(&prop);
 	return process_measurement(file, current_cred(), &prop, NULL, 0,
 				   mask & (MAY_READ | MAY_WRITE | MAY_EXEC |
-					   MAY_APPEND), FILE_CHECK);
+					   MAY_APPEND), FILE_CHECK, 0);
 }
 
 static int __ima_inode_hash(struct inode *inode, struct file *file, char *buf,
@@ -874,12 +881,13 @@ static int ima_read_file(struct file *file, enum kernel_read_file_id read_id,
 	func = read_idmap[read_id] ?: FILE_CHECK;
 	security_current_getlsmprop_subj(&prop);
 	return process_measurement(file, current_cred(), &prop, NULL, 0,
-				   MAY_READ, func);
+				   MAY_READ, func, 0);
 }
 
 const int read_idmap[READING_MAX_ID] = {
 	[READING_FIRMWARE] = FIRMWARE_CHECK,
 	[READING_MODULE] = MODULE_CHECK,
+	[READING_MODULE_COMPRESSED] = MODULE_CHECK,
 	[READING_KEXEC_IMAGE] = KEXEC_KERNEL_CHECK,
 	[READING_KEXEC_INITRAMFS] = KEXEC_INITRAMFS_CHECK,
 	[READING_POLICY] = POLICY_CHECK
@@ -917,7 +925,7 @@ static int ima_post_read_file(struct file *file, char *buf, loff_t size,
 	func = read_idmap[read_id] ?: FILE_CHECK;
 	security_current_getlsmprop_subj(&prop);
 	return process_measurement(file, current_cred(), &prop, buf, size,
-				   MAY_READ, func);
+				   MAY_READ, func, read_id);
 }
 
 /**