restrict reading from /proc/<pid>/maps to those who share ->mm or can ptrace pid

Contents of /proc/*/maps is sensitive and may become sensitive after
open() (e.g.  if target originally shares our ->mm and later does exec
on suid-root binary).

Check at read() (actually, ->start() of iterator) time that mm_struct
we'd grabbed and locked is
 - still the ->mm of target
 - equal to reader's ->mm or the target is ptracable by reader.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 3 deletions

diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index d8b8c7183c24..1932c2ca3457 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -165,15 +165,13 @@ static void *m_start(struct seq_file *m, loff_t *pos)
         if (!priv->task)
                 return NULL;
 
-        mm = get_task_mm(priv->task);
+        mm = mm_for_maps(priv->task);
         if (!mm) {
                 put_task_struct(priv->task);
                 priv->task = NULL;
                 return NULL;
         }
 
-        down_read(&mm->mmap_sem);
-
         /* start from the Nth VMA */
         for (vml = mm->context.vmlist; vml; vml = vml->next)
                 if (n-- == 0)