diff options
author | Jann Horn <jannh@google.com> | 2018-06-25 18:34:19 +0200 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-09-09 20:04:35 +0200 |
commit | 3d4c43c8f0fb00ad5f58c06b382dc2dc769a63e1 (patch) | |
tree | 392fe15adb0bea50993207914da8dd800aa3b2e1 /kernel | |
parent | 5c16a16fcf03789baddd43fe4ca734b4c2877db3 (diff) |
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 <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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/user_namespace.c | 39 |
1 files changed, 19 insertions, 20 deletions
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; |