/proc/*/environ: wrong placing of ptrace_may_attach() check

It's a bit dopey-looking and can permit a task to cause a pagefault in an mm
which it doesn't have permission to read from.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 46ea5d56e1bb..d0921944e68c 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -204,12 +204,17 @@ static int proc_pid_environ(struct task_struct *task, char * buffer)
         int res = 0;
         struct mm_struct *mm = get_task_mm(task);
         if (mm) {
-                unsigned int len = mm->env_end - mm->env_start;
+                unsigned int len;
+
+                res = -ESRCH;
+                if (!ptrace_may_attach(task))
+                        goto out;
+
+                len  = mm->env_end - mm->env_start;
                 if (len > PAGE_SIZE)
                         len = PAGE_SIZE;
                 res = access_process_vm(task, mm->env_start, buffer, len, 0);
-                if (!ptrace_may_attach(task))
-                        res = -ESRCH;
+out:
                 mmput(mm);
         }
         return res;