From d5e7b3c5f51fc6d34e12b6d87bfd30ab277c4625 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Tue, 31 Oct 2017 17:09:34 -0500 Subject: userns: Don't read extents twice in m_start This is important so reading /proc//{uid_map,gid_map,projid_map} while the map is being written does not do strange things. Signed-off-by: "Eric W. Biederman" --- kernel/user_namespace.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 563a2981d7c7..4f7e357ac1e2 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -683,11 +683,13 @@ static void *m_start(struct seq_file *seq, loff_t *ppos, struct uid_gid_map *map) { loff_t pos = *ppos; + unsigned extents = map->nr_extents; + smp_rmb(); - if (pos >= map->nr_extents) + if (pos >= extents) return NULL; - if (map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS) + if (extents <= UID_GID_MAP_MAX_BASE_EXTENTS) return &map->extent[pos]; return &map->forward[pos]; -- cgit v1.2.3