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>

1 files changed, 6 insertions, 4 deletions

diff --git a/fs/exec.c b/fs/exec.c
index d51f7172832b..a4cfd1d725e0 100644
--- 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;