4.18-stable review patch. If anyone has any objections, please let me know.
------------------ From: Jann Horn <[email protected]> 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: [email protected] Signed-off-by: Jann Horn <[email protected]> Acked-by: Christian Brauner <[email protected]> Acked-by: Serge Hallyn <[email protected]> Signed-off-by: Eric W. Biederman <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/user_namespace.c | 24 ++++++++++-------------- 1 file changed, 10 insertions(+), 14 deletions(-) --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -859,7 +859,16 @@ static ssize_t map_write(struct file *fi 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 *fi 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;
