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, 2 insertions, 2 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 7c76f2ffaeaa..0c65d306f412 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -120,7 +120,7 @@ int ptrace_check_attach(struct task_struct *child, int kill)
         return ret;
 }
 
-static int may_attach(struct task_struct *task)
+int __ptrace_may_attach(struct task_struct *task)
 {
         /* May we inspect the given task?
          * This check is used both for attaching with ptrace
@@ -154,7 +154,7 @@ int ptrace_may_attach(struct task_struct *task)
 {
         int err;
         task_lock(task);
-        err = may_attach(task);
+        err = __ptrace_may_attach(task);
         task_unlock(task);
         return !err;
 }