io-wq: inherit audit loginuid and sessionid

Make sure the async io-wq workers inherit the loginuid and sessionid from
the original task, and restore them to unset once we're done with the
async work item.

While at it, disable the ability for kernel threads to write to their own
loginuid.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io-wq.c

@@ -18,6 +18,7 @@
 #include <linux/fs_struct.h>
 #include <linux/task_work.h>
 #include <linux/blk-cgroup.h>
+#include <linux/audit.h>
 
 #include "io-wq.h"
 
@@ -484,6 +485,10 @@ static void io_impersonate_work(struct io_worker *worker,
 		io_wq_switch_creds(worker, work);
 	current->signal->rlim[RLIMIT_FSIZE].rlim_cur = work->identity->fsize;
 	io_wq_switch_blkcg(worker, work);
+#ifdef CONFIG_AUDIT
+	current->loginuid = work->identity->loginuid;
+	current->sessionid = work->identity->sessionid;
+#endif
 }
 
 static void io_assign_current_work(struct io_worker *worker,
@@ -496,6 +501,11 @@ static void io_assign_current_work(struct io_worker *worker,
 		cond_resched();
 	}
 
+#ifdef CONFIG_AUDIT
+	current->loginuid = KUIDT_INIT(AUDIT_UID_UNSET);
+	current->sessionid = AUDIT_SID_UNSET;
+#endif
+
 	spin_lock_irq(&worker->lock);
 	worker->cur_work = work;
 	spin_unlock_irq(&worker->lock);

fs/io_uring.c

@@ -81,6 +81,7 @@
 #include <linux/pagemap.h>
 #include <linux/io_uring.h>
 #include <linux/blk-cgroup.h>
+#include <linux/audit.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/io_uring.h>
@@ -327,6 +328,11 @@ struct io_ring_ctx {
 
 	const struct cred	*creds;
 
+#ifdef CONFIG_AUDIT
+	kuid_t			loginuid;
+	unsigned int		sessionid;
+#endif
+
 	struct completion	ref_comp;
 	struct completion	sq_thread_comp;
 
@@ -1057,6 +1063,10 @@ static void io_init_identity(struct io_identity *id)
 	id->nsproxy = current->nsproxy;
 	id->fs = current->fs;
 	id->fsize = rlimit(RLIMIT_FSIZE);
+#ifdef CONFIG_AUDIT
+	id->loginuid = current->loginuid;
+	id->sessionid = current->sessionid;
+#endif
 	refcount_set(&id->count, 1);
 }
 
@@ -1316,6 +1326,11 @@ static bool io_grab_identity(struct io_kiocb *req)
 		get_cred(id->creds);
 		req->work.flags |= IO_WQ_WORK_CREDS;
 	}
+#ifdef CONFIG_AUDIT
+	if (!uid_eq(current->loginuid, id->loginuid) ||
+	    current->sessionid != id->sessionid)
+		return false;
+#endif
 	if (!(req->work.flags & IO_WQ_WORK_FS) &&
 	    (def->work_flags & IO_WQ_WORK_FS)) {
 		if (current->fs != id->fs)
@@ -6755,6 +6770,10 @@ static int io_sq_thread(void *data)
 				old_cred = override_creds(ctx->creds);
 			}
 			io_sq_thread_associate_blkcg(ctx, &cur_css);
+#ifdef CONFIG_AUDIT
+			current->loginuid = ctx->loginuid;
+			current->sessionid = ctx->sessionid;
+#endif
 
 			ret |= __io_sq_thread(ctx, start_jiffies, cap_entries);
 
@@ -9203,7 +9222,10 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p,
 	ctx->compat = in_compat_syscall();
 	ctx->user = user;
 	ctx->creds = get_current_cred();
-
+#ifdef CONFIG_AUDIT
+	ctx->loginuid = current->loginuid;
+	ctx->sessionid = current->sessionid;
+#endif
 	ctx->sqo_task = get_task_struct(current);
 
 	/*

fs/proc/base.c

@@ -1268,6 +1268,10 @@ static ssize_t proc_loginuid_write(struct file * file, const char __user * buf,
 	kuid_t kloginuid;
 	int rv;
 
+	/* Don't let kthreads write their own loginuid */
+	if (current->flags & PF_KTHREAD)
+		return -EPERM;
+
 	rcu_read_lock();
 	if (current != pid_task(proc_pid(inode), PIDTYPE_PID)) {
 		rcu_read_unlock();

include/linux/io_uring.h

@@ -15,6 +15,10 @@ struct io_identity {
 	struct nsproxy			*nsproxy;
 	struct fs_struct		*fs;
 	unsigned long			fsize;
+#ifdef CONFIG_AUDIT
+	kuid_t				loginuid;
+	unsigned int			sessionid;
+#endif
 	refcount_t			count;
 };