[PATCH] sanitize unshare_files/reset_files_struct

* let unshare_files() give caller the displaced files_struct
* don't bother with grabbing reference only to drop it in the
  caller if it hadn't been shared in the first place
* in that form unshare_files() is trivially implemented via
  unshare_fd(), so we eliminate the duplicate logics in fork.c
* reset_files_struct() is not just only called for current;
  it will break the system if somebody ever calls it for anything
  else (we can't modify ->files of somebody else).  Lose the
  task_struct * argument.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 6 insertions, 12 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 475543002f13..b152029f18f6 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1269,19 +1269,13 @@ int do_execve(char * filename,
         struct linux_binprm *bprm;
         struct file *file;
         unsigned long env_p;
-        struct files_struct *files;
+        struct files_struct *displaced;
         int retval;
 
-        files = current->files;
-        retval = unshare_files();
+        retval = unshare_files(&displaced);
         if (retval)
                 goto out_ret;
 
-        if (files == current->files) {
-                put_files_struct(files);
-                files = NULL;
-        }
-
         retval = -ENOMEM;
         bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
         if (!bprm)
@@ -1340,8 +1334,8 @@ int do_execve(char * filename,
                 security_bprm_free(bprm);
                 acct_update_integrals(current);
                 kfree(bprm);
-                if (files)
-                        put_files_struct(files);
+                if (displaced)
+                        put_files_struct(displaced);
                 return retval;
         }
 
@@ -1363,8 +1357,8 @@ out_kfree:
         kfree(bprm);
 
 out_files:
-        if (files)
-                reset_files_struct(current, files);
+        if (displaced)
+                reset_files_struct(displaced);
 out_ret:
         return retval;
 }