3.18-stable review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
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
--- kernel/user_namespace.c | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-)
--- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -602,7 +602,16 @@ static ssize_t map_write(struct file *fi struct uid_gid_extent *extent = NULL; unsigned long page = 0; 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; + + /* Slurp in the user data */ + if (copy_from_user(kbuf, buf, count)) + return -EFAULT; + kbuf[count] = '\0';
/* * The userns_state_mutex serializes all writes to any given map. @@ -643,17 +652,6 @@ static ssize_t map_write(struct file *fi 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;