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, 20 insertions, 0 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 02a63ac04178..7411bfb0b7cc 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -202,6 +202,26 @@ static int proc_root_link(struct inode *inode, struct dentry **dentry, struct vf
          (task->state == TASK_STOPPED || task->state == TASK_TRACED) && \
          security_ptrace(current,task) == 0))
 
+struct mm_struct *mm_for_maps(struct task_struct *task)
+{
+        struct mm_struct *mm = get_task_mm(task);
+        if (!mm)
+                return NULL;
+        down_read(&mm->mmap_sem);
+        task_lock(task);
+        if (task->mm != mm)
+                goto out;
+        if (task->mm != current->mm && __ptrace_may_attach(task) < 0)
+                goto out;
+        task_unlock(task);
+        return mm;
+out:
+        task_unlock(task);
+        up_read(&mm->mmap_sem);
+        mmput(mm);
+        return NULL;
+}
+
 static int proc_pid_cmdline(struct task_struct *task, char * buffer)
 {
         int res = 0;