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Commit 5820f140 authored by Jann Horn's avatar Jann Horn Committed by Eric W. Biederman
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userns: move user access out of the mutex 



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: 22d917d8 ("userns: Rework the user_namespace adding uid/gid...")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarJann Horn <jannh@google.com>
Acked-by: default avatarChristian Brauner <christian@brauner.io>
Acked-by: default avatarSerge Hallyn <serge@hallyn.com>
Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
parent 355139a8

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;