userns: move user access out of the mutex (5820f140) · Commits · 戴 / test

The old code would hold the userns_state_mutex indefinitely if memdup_user_nul stalled due to e.g. a userfault region. Prevent that by moving the memdup_user_nul in front of the mutex_lock(). Note: This changes the error precedence of invalid buf/count/*ppos vs map already written / capabilities missing. Fixes: ("userns: Rework the user_namespace adding uid/gid...") Cc: stable@vger.kernel.org Signed-off-by:

Jann Horn <jannh@google.com> Acked-by:

Christian Brauner <christian@brauner.io> Acked-by:

Serge Hallyn <serge@hallyn.com> Signed-off-by:

Eric W. Biederman <ebiederm@xmission.com>

kernel/user_namespace.c

+10 −14

Original line number	Diff line number	Diff line
		@@ -859,7 +859,16 @@ static ssize_t map_write(struct file file, const char __user buf,
		unsigned idx;
		struct uid_gid_extent extent;
		char kbuf = NULL, pos, *next_line;
		ssize_t ret = -EINVAL;
		ssize_t ret;

		/* Only allow < page size writes at the beginning of the file */
		if ((*ppos != 0) \|\| (count >= PAGE_SIZE))
		return -EINVAL;

		/* Slurp in the user data */
		kbuf = memdup_user_nul(buf, count);
		if (IS_ERR(kbuf))
		return PTR_ERR(kbuf);

		/*
		* The userns_state_mutex serializes all writes to any given map.
		@@ -895,19 +904,6 @@ static ssize_t map_write(struct file file, const char __user buf,
		if (cap_valid(cap_setid) && !file_ns_capable(file, ns, CAP_SYS_ADMIN))
		goto out;

		/* Only allow < page size writes at the beginning of the file */
		ret = -EINVAL;
		if ((*ppos != 0) \|\| (count >= PAGE_SIZE))
		goto out;

		/* Slurp in the user data */
		kbuf = memdup_user_nul(buf, count);
		if (IS_ERR(kbuf)) {
		ret = PTR_ERR(kbuf);
		kbuf = NULL;
		goto out;
		}

		/* Parse the user data */
		ret = -EINVAL;
		pos = kbuf;

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