exec: move allow_write_access/fput to exec_binprm()

When search_binary_handler() succeeds it does allow_write_access() and
fput(), then it clears bprm->file to ensure the caller will not do the
same.

We can simply move this code to exec_binprm() which is called only once.
In fact we could move this to free_bprm() and remove the same code in
do_execve_common's error path.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Zach Levis <zml@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/exec.c b/fs/exec.c
index d51f717..a4cfd1d 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1400,10 +1400,6 @@ int search_binary_handler(struct linux_binprm *bprm)
                        bprm->recursion_depth--;
                        if (retval >= 0) {
                                put_binfmt(fmt);
-                               allow_write_access(bprm->file);
-                               if (bprm->file)
-                                       fput(bprm->file);
-                               bprm->file = NULL;
                                return retval;
                        }
                        read_lock(&binfmt_lock);
@@ -1455,6 +1451,12 @@ static int exec_binprm(struct linux_binprm *bprm)
                ptrace_event(PTRACE_EVENT_EXEC, old_vpid);
                current->did_exec = 1;
                proc_exec_connector(current);
+
+               if (bprm->file) {
+                       allow_write_access(bprm->file);
+                       fput(bprm->file);
+                       bprm->file = NULL; /* to catch use-after-free */
+               }
        }
 
        return ret;