From 3d4c43c8f0fb00ad5f58c06b382dc2dc769a63e1 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Mon, 25 Jun 2018 18:34:19 +0200 Subject: userns: move user access out of the mutex commit 5820f140edef111a9ea2ef414ab2428b8cb805b1 upstream. 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: 22d917d80e84 ("userns: Rework the user_namespace adding uid/gid...") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn Acked-by: Christian Brauner Acked-by: Serge Hallyn Signed-off-by: Eric W. Biederman Signed-off-by: Greg Kroah-Hartman --- kernel/user_namespace.c | 39 +++++++++++++++++++-------------------- 1 file changed, 19 insertions(+), 20 deletions(-) (limited to 'kernel') diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 88fefa68c516..a965df4b54f5 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -602,9 +602,26 @@ static ssize_t map_write(struct file *file, const char __user *buf, struct uid_gid_map new_map; unsigned idx; struct uid_gid_extent *extent = NULL; - unsigned long page = 0; + unsigned long page; char *kbuf, *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; + + /* Get a buffer */ + page = __get_free_page(GFP_TEMPORARY); + kbuf = (char *) page; + if (!page) + return -ENOMEM; + + /* Slurp in the user data */ + if (copy_from_user(kbuf, buf, count)) { + free_page(page); + return -EFAULT; + } + kbuf[count] = '\0'; /* * The userns_state_mutex serializes all writes to any given map. @@ -638,24 +655,6 @@ 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; - /* Get a buffer */ - ret = -ENOMEM; - page = __get_free_page(GFP_TEMPORARY); - kbuf = (char *) page; - if (!page) - 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 */ - ret = -EFAULT; - if (copy_from_user(kbuf, buf, count)) - goto out; - kbuf[count] = '\0'; - /* Parse the user data */ ret = -EINVAL; pos = kbuf; -- cgit v1.2.3