[PATCH v10 5/9] Reimplement RLIMIT_MSGQUEUE on top of ucounts

Alexey Gladkov gladkov.alexey at gmail.com
Wed Apr 7 17:08:10 UTC 2021


The rlimit counter is tied to uid in the user_namespace. This allows
rlimit values to be specified in userns even if they are already
globally exceeded by the user. However, the value of the previous
user_namespaces cannot be exceeded.

Signed-off-by: Alexey Gladkov <gladkov.alexey at gmail.com>
---
 include/linux/sched/user.h     |  4 ----
 include/linux/user_namespace.h |  1 +
 ipc/mqueue.c                   | 41 ++++++++++++++++++----------------
 kernel/fork.c                  |  1 +
 kernel/ucount.c                |  1 +
 kernel/user_namespace.c        |  1 +
 6 files changed, 26 insertions(+), 23 deletions(-)

diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index d33d867ad6c1..8a34446681aa 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -18,10 +18,6 @@ struct user_struct {
 #endif
 #ifdef CONFIG_EPOLL
 	atomic_long_t epoll_watches; /* The number of file descriptors currently watched */
-#endif
-#ifdef CONFIG_POSIX_MQUEUE
-	/* protected by mq_lock	*/
-	unsigned long mq_bytes;	/* How many bytes can be allocated to mqueue? */
 #endif
 	unsigned long locked_shm; /* How many pages of mlocked shm ? */
 	unsigned long unix_inflight;	/* How many files in flight in unix sockets */
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 9d1ca370c201..d0fea0306394 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -51,6 +51,7 @@ enum ucount_type {
 	UCOUNT_INOTIFY_WATCHES,
 #endif
 	UCOUNT_RLIMIT_NPROC,
+	UCOUNT_RLIMIT_MSGQUEUE,
 	UCOUNT_COUNTS,
 };
 
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 8031464ed4ae..f0f8f013dae2 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -144,7 +144,7 @@ struct mqueue_inode_info {
 	struct pid *notify_owner;
 	u32 notify_self_exec_id;
 	struct user_namespace *notify_user_ns;
-	struct user_struct *user;	/* user who created, for accounting */
+	struct ucounts *ucounts;	/* user who created, for accounting */
 	struct sock *notify_sock;
 	struct sk_buff *notify_cookie;
 
@@ -292,7 +292,6 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 		struct ipc_namespace *ipc_ns, umode_t mode,
 		struct mq_attr *attr)
 {
-	struct user_struct *u = current_user();
 	struct inode *inode;
 	int ret = -ENOMEM;
 
@@ -321,7 +320,7 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 		info->notify_owner = NULL;
 		info->notify_user_ns = NULL;
 		info->qsize = 0;
-		info->user = NULL;	/* set when all is ok */
+		info->ucounts = NULL;	/* set when all is ok */
 		info->msg_tree = RB_ROOT;
 		info->msg_tree_rightmost = NULL;
 		info->node_cache = NULL;
@@ -371,19 +370,24 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 		if (mq_bytes + mq_treesize < mq_bytes)
 			goto out_inode;
 		mq_bytes += mq_treesize;
-		spin_lock(&mq_lock);
-		if (u->mq_bytes + mq_bytes < u->mq_bytes ||
-		    u->mq_bytes + mq_bytes > rlimit(RLIMIT_MSGQUEUE)) {
+		info->ucounts = get_ucounts(current_ucounts());
+		if (info->ucounts) {
+			bool overlimit;
+
+			spin_lock(&mq_lock);
+			overlimit = inc_rlimit_ucounts_and_test(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE,
+					mq_bytes, rlimit(RLIMIT_MSGQUEUE));
+			if (overlimit) {
+				dec_rlimit_ucounts(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE, mq_bytes);
+				spin_unlock(&mq_lock);
+				put_ucounts(info->ucounts);
+				info->ucounts = NULL;
+				/* mqueue_evict_inode() releases info->messages */
+				ret = -EMFILE;
+				goto out_inode;
+			}
 			spin_unlock(&mq_lock);
-			/* mqueue_evict_inode() releases info->messages */
-			ret = -EMFILE;
-			goto out_inode;
 		}
-		u->mq_bytes += mq_bytes;
-		spin_unlock(&mq_lock);
-
-		/* all is ok */
-		info->user = get_uid(u);
 	} else if (S_ISDIR(mode)) {
 		inc_nlink(inode);
 		/* Some things misbehave if size == 0 on a directory */
@@ -497,7 +501,6 @@ static void mqueue_free_inode(struct inode *inode)
 static void mqueue_evict_inode(struct inode *inode)
 {
 	struct mqueue_inode_info *info;
-	struct user_struct *user;
 	struct ipc_namespace *ipc_ns;
 	struct msg_msg *msg, *nmsg;
 	LIST_HEAD(tmp_msg);
@@ -520,8 +523,7 @@ static void mqueue_evict_inode(struct inode *inode)
 		free_msg(msg);
 	}
 
-	user = info->user;
-	if (user) {
+	if (info->ucounts) {
 		unsigned long mq_bytes, mq_treesize;
 
 		/* Total amount of bytes accounted for the mqueue */
@@ -533,7 +535,7 @@ static void mqueue_evict_inode(struct inode *inode)
 					  info->attr.mq_msgsize);
 
 		spin_lock(&mq_lock);
-		user->mq_bytes -= mq_bytes;
+		dec_rlimit_ucounts(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE, mq_bytes);
 		/*
 		 * get_ns_from_inode() ensures that the
 		 * (ipc_ns = sb->s_fs_info) is either a valid ipc_ns
@@ -543,7 +545,8 @@ static void mqueue_evict_inode(struct inode *inode)
 		if (ipc_ns)
 			ipc_ns->mq_queues_count--;
 		spin_unlock(&mq_lock);
-		free_uid(user);
+		put_ucounts(info->ucounts);
+		info->ucounts = NULL;
 	}
 	if (ipc_ns)
 		put_ipc_ns(ipc_ns);
diff --git a/kernel/fork.c b/kernel/fork.c
index d8a4956463ae..85c6094f5a48 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -823,6 +823,7 @@ void __init fork_init(void)
 		init_user_ns.ucount_max[i] = max_threads/2;
 
 	init_user_ns.ucount_max[UCOUNT_RLIMIT_NPROC] = task_rlimit(&init_task, RLIMIT_NPROC);
+	init_user_ns.ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = task_rlimit(&init_task, RLIMIT_MSGQUEUE);
 
 #ifdef CONFIG_VMAP_STACK
 	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
diff --git a/kernel/ucount.c b/kernel/ucount.c
index d2c2f991ab3e..3f1682b690e6 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -80,6 +80,7 @@ static struct ctl_table user_table[] = {
 	UCOUNT_ENTRY("max_inotify_instances"),
 	UCOUNT_ENTRY("max_inotify_watches"),
 #endif
+	{ },
 	{ },
 	{ }
 };
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 2434b13b02e5..cc90d5203acf 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -122,6 +122,7 @@ int create_user_ns(struct cred *new)
 		ns->ucount_max[i] = INT_MAX;
 	}
 	ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC);
+	ns->ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = rlimit(RLIMIT_MSGQUEUE);
 	ns->ucounts = ucounts;
 
 	/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */
-- 
2.29.3



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