[PATCH v2] IMA: make runtime measurement list pollable

[Daiki Ueno <dueno@xxxxxxxxxx>]

Currently it's not possible to efficiently monitor changes to the IMA
runtime measurement list with poll().  While ascii_runtime_measurement
file is pollable with POLLIN, it returns immediately even if there is
no change to the list, and thus cannot be used as a wait condition in
a loop.

This patch makes it possible to poll the file in a similar fashion to
the sysfs files: POLLIN is still always signalled, while POLLPRI will
also be signalled on actual changes made to the list.

Signed-off-by: Daiki Ueno <dueno@xxxxxxxxxx>
---
v2: moved wake_up_interruptible() call after PCR extend and expanded
the patch description to cover the use-case, suggested by Mimi.
---
 security/integrity/ima/ima.h       |  2 ++
 security/integrity/ima/ima_fs.c    | 22 ++++++++++++++++++++++
 security/integrity/ima/ima_queue.c |  8 +++++++-
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index be965a8715e4..a7070a74a7ff 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -180,6 +180,8 @@ struct ima_h_table {
 };
 extern struct ima_h_table ima_htable;
 
+extern wait_queue_head_t ima_htable_wait;
+
 static inline unsigned int ima_hash_key(u8 *digest)
 {
 	/* there is no point in taking a hash of part of a digest */
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 3d8e9d5db5aa..f8741784217d 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -21,6 +21,7 @@
 #include <linux/rcupdate.h>
 #include <linux/parser.h>
 #include <linux/vmalloc.h>
+#include <linux/poll.h>
 
 #include "ima.h"
 
@@ -198,11 +199,31 @@ static int ima_measurements_open(struct inode *inode, struct file *file)
 	return seq_open(file, &ima_measurments_seqops);
 }
 
+static __poll_t ima_measurements_poll(struct file *file, poll_table *wait)
+{
+	struct seq_file *seq = file->private_data;
+	/* always allow reading */
+	__poll_t mask = EPOLLIN | EPOLLRDNORM;
+	int event;
+
+	poll_wait(file, &ima_htable_wait, wait);
+
+	event = atomic_long_read(&ima_htable.len);
+
+	if (seq->poll_event != event) {
+		seq->poll_event = event;
+		mask |= EPOLLERR | EPOLLPRI;
+	}
+
+	return mask;
+}
+
 static const struct file_operations ima_measurements_ops = {
 	.open = ima_measurements_open,
 	.read = seq_read,
 	.llseek = seq_lseek,
 	.release = seq_release,
+	.poll = ima_measurements_poll,
 };
 
 void ima_print_digest(struct seq_file *m, u8 *digest, u32 size)
@@ -269,6 +290,7 @@ static const struct file_operations ima_ascii_measurements_ops = {
 	.read = seq_read,
 	.llseek = seq_lseek,
 	.release = seq_release,
+	.poll = ima_measurements_poll,
 };
 
 static ssize_t ima_read_policy(char *path)
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 532da87ce519..de4941909a93 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -38,6 +38,9 @@ struct ima_h_table ima_htable = {
 	.queue[0 ... IMA_MEASURE_HTABLE_SIZE - 1] = HLIST_HEAD_INIT
 };
 
+/* wait queue for polling changes in ima_htable */
+DECLARE_WAIT_QUEUE_HEAD(ima_htable_wait);
+
 /* mutex protects atomicity of extending measurement list
  * and extending the TPM PCR aggregate. Since tpm_extend can take
  * long (and the tpm driver uses a mutex), we can't use the spinlock.
@@ -119,6 +122,7 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
 		binary_runtime_size = (binary_runtime_size < ULONG_MAX - size) ?
 		     binary_runtime_size + size : ULONG_MAX;
 	}
+
 	return 0;
 }
 
@@ -193,9 +197,11 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
 			 tpmresult);
 		audit_cause = tpm_audit_cause;
 		audit_info = 0;
-	}
+	} else
+		wake_up_interruptible(&ima_htable_wait);
 out:
 	mutex_unlock(&ima_extend_list_mutex);
+
 	integrity_audit_msg(AUDIT_INTEGRITY_PCR, inode, filename,
 			    op, audit_cause, result, audit_info);
 	return result;
-- 
2.31.1