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userns: Don't read extents twice in m_start

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This is important so reading /proc/<pid>/{uid_map,gid_map,projid_map} while
the map is being written does not do strange things.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2017-10-31 17:09:34 -05:00
parent 3edf652fa1
commit d5e7b3c5f5
1 changed files with 4 additions and 2 deletions
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6
kernel/user_namespace.c
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@ -683,11 +683,13 @@ static void *m_start(struct seq_file *seq, loff_t *ppos,
struct uid_gid_map *map) struct uid_gid_map *map)
{ {
loff_t pos = *ppos; loff_t pos = *ppos;
unsigned extents = map->nr_extents;
smp_rmb();
if (pos >= map->nr_extents) if (pos >= extents)
return NULL; 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->extent[pos];
return &map->forward[pos]; return &map->forward[pos];