c/r: prctl: less paranoid prctl_set_mm_exe_file()

"no other files mapped" requirement from my previous patch (c/r: prctl:
update prctl_set_mm_exe_file() after mm->num_exe_file_vmas removal) is too
paranoid, it forbids operation even if there mapped one shared-anon vma.

Let's check that current mm->exe_file already unmapped, in this case
exe_file symlink already outdated and its changing is reasonable.

Plus, this patch fixes exit code in case operation success.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Reported-by: Cyrill Gorcunov <gorcunov@openvz.org>
Tested-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 6 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index e0c8ffc50d7f..2d39a84cd857 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1788,7 +1788,6 @@ SYSCALL_DEFINE1(umask, int, mask)
 #ifdef CONFIG_CHECKPOINT_RESTORE
 static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
 {
-        struct vm_area_struct *vma;
         struct file *exe_file;
         struct dentry *dentry;
         int err;
@@ -1816,13 +1815,17 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
         down_write(&mm->mmap_sem);
 
         /*
-         * Forbid mm->exe_file change if there are mapped other files.
+         * Forbid mm->exe_file change if old file still mapped.
          */
         err = -EBUSY;
-        for (vma = mm->mmap; vma; vma = vma->vm_next) {
-                if (vma->vm_file && !path_equal(&vma->vm_file->f_path,
-                                                &exe_file->f_path))
-                        goto exit_unlock;
+        if (mm->exe_file) {
+                struct vm_area_struct *vma;
+
+                for (vma = mm->mmap; vma; vma = vma->vm_next)
+                        if (vma->vm_file &&
+                            path_equal(&vma->vm_file->f_path,
+                                       &mm->exe_file->f_path))
+                                goto exit_unlock;
         }
 
         /*
@@ -1835,6 +1838,7 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
         if (test_and_set_bit(MMF_EXE_FILE_CHANGED, &mm->flags))
                 goto exit_unlock;
 
+        err = 0;
         set_mm_exe_file(mm, exe_file);
 exit_unlock:
         up_write(&mm->mmap_sem);