[PATCH] sanitize handling of shared descriptor tables in failing execve()

* unshare_files() can fail; doing it after irreversible actions is wrong
  and de_thread() is certainly irreversible.
* since we do it unconditionally anyway, we might as well do it in do_execve()
  and save ourselves the PITA in binfmt handlers, etc.
* while we are at it, binfmt_som actually leaked files_struct on failure.

As a side benefit, unshare_files(), put_files_struct() and reset_files_struct()
become unexported.

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

1 files changed, 18 insertions, 16 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 54a0a557b678..475543002f13 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -953,7 +953,6 @@ int flush_old_exec(struct linux_binprm * bprm)
 {
         char * name;
         int i, ch, retval;
-        struct files_struct *files;
         char tcomm[sizeof(current->comm)];
 
         /*
@@ -965,26 +964,15 @@ int flush_old_exec(struct linux_binprm * bprm)
                 goto out;
 
         /*
-         * Make sure we have private file handles. Ask the
-         * fork helper to do the work for us and the exit
-         * helper to do the cleanup of the old one.
-         */
-        files = current->files;         /* refcounted so safe to hold */
-        retval = unshare_files();
-        if (retval)
-                goto out;
-        /*
          * Release all of the old mmap stuff
          */
         retval = exec_mmap(bprm->mm);
         if (retval)
-                goto mmap_failed;
+                goto out;
 
         bprm->mm = NULL;                /* We're using it now */
 
         /* This is the point of no return */
-        put_files_struct(files);
-
         current->sas_ss_sp = current->sas_ss_size = 0;
 
         if (current->euid == current->uid && current->egid == current->gid)
@@ -1034,8 +1022,6 @@ int flush_old_exec(struct linux_binprm * bprm)
 
         return 0;
 
-mmap_failed:
-        reset_files_struct(current, files);
 out:
         return retval;
 }
@@ -1283,12 +1269,23 @@ int do_execve(char * filename,
         struct linux_binprm *bprm;
         struct file *file;
         unsigned long env_p;
+        struct files_struct *files;
         int retval;
 
+        files = current->files;
+        retval = unshare_files();
+        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)
-                goto out_ret;
+                goto out_files;
 
         file = open_exec(filename);
         retval = PTR_ERR(file);
@@ -1343,6 +1340,8 @@ int do_execve(char * filename,
                 security_bprm_free(bprm);
                 acct_update_integrals(current);
                 kfree(bprm);
+                if (files)
+                        put_files_struct(files);
                 return retval;
         }
 
@@ -1363,6 +1362,9 @@ out_file:
 out_kfree:
         kfree(bprm);
 
+out_files:
+        if (files)
+                reset_files_struct(current, files);
 out_ret:
         return retval;
 }