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, 2 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index c24d81a5a04..8043a3eab52 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -397,12 +397,11 @@ 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)
                 return NULL;
 
         priv->tail_vma = tail_vma = get_gate_vma(priv->task);
-        down_read(&mm->mmap_sem);
 
         /* Start with last addr hint */
         if (last_addr && (vma = find_vma(mm, last_addr))) {