[RFC PATCH ghak90 (was ghak32) V3 09/10] debug audit: read container ID of a process

[Richard Guy Briggs <rgb@redhat.com>]

Add support for reading the audit container identifier from the proc
filesystem.

This is a read from the proc entry of the form
/proc/PID/audit_containerid where PID is the process ID of the task
whose audit container identifier is sought.

The read expects up to a u64 value (unset: 18446744073709551615).

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
---
 fs/proc/base.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 318dff4..ca8bfe2 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1303,6 +1303,21 @@ static ssize_t proc_sessionid_read(struct file * file, char __user * buf,
 	.llseek		= generic_file_llseek,
 };
 
+static ssize_t proc_contid_read(struct file *file, char __user *buf,
+				  size_t count, loff_t *ppos)
+{
+	struct inode *inode = file_inode(file);
+	struct task_struct *task = get_proc_task(inode);
+	ssize_t length;
+	char tmpbuf[TMPBUFLEN*2];
+
+	if (!task)
+		return -ESRCH;
+	length = scnprintf(tmpbuf, TMPBUFLEN*2, "%llu", audit_get_contid(task));
+	put_task_struct(task);
+	return simple_read_from_buffer(buf, count, ppos, tmpbuf, length);
+}
+
 static ssize_t proc_contid_write(struct file *file, const char __user *buf,
 				   size_t count, loff_t *ppos)
 {
@@ -1333,6 +1348,7 @@ static ssize_t proc_contid_write(struct file *file, const char __user *buf,
 }
 
 static const struct file_operations proc_contid_operations = {
+	.read		= proc_contid_read,
 	.write		= proc_contid_write,
 	.llseek		= generic_file_llseek,
 };
@@ -3030,7 +3046,7 @@ static int proc_pid_patch_state(struct seq_file *m, struct pid_namespace *ns,
 #ifdef CONFIG_AUDITSYSCALL
 	REG("loginuid",   S_IWUSR|S_IRUGO, proc_loginuid_operations),
 	REG("sessionid",  S_IRUGO, proc_sessionid_operations),
-	REG("audit_containerid", S_IWUSR, proc_contid_operations),
+	REG("audit_containerid", S_IWUSR|S_IRUSR, proc_contid_operations),
 #endif
 #ifdef CONFIG_FAULT_INJECTION
 	REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),
@@ -3422,7 +3438,7 @@ static int proc_tid_comm_permission(struct inode *inode, int mask)
 #ifdef CONFIG_AUDITSYSCALL
 	REG("loginuid",  S_IWUSR|S_IRUGO, proc_loginuid_operations),
 	REG("sessionid",  S_IRUGO, proc_sessionid_operations),
-	REG("audit_containerid", S_IWUSR, proc_contid_operations),
+	REG("audit_containerid", S_IWUSR|S_IRUSR, proc_contid_operations),
 #endif
 #ifdef CONFIG_FAULT_INJECTION
 	REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),
-- 
1.8.3.1