Hi Kees,
Why not add a new file flag instead ?
Something like this (editing your patch by hand to illustrate) :
diff --git a/fs/file_table.c b/fs/file_table.c
index ad17e05ebf95..3a7eee76ea90 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -191,6 +191,17 @@ static void __fput(struct file *file)
might_sleep();
+ /*
+ * XXX: While avoiding mmap_sem, we've already been written to.
+ * We must ignore the return value, since we can't reject the
+ * write.
+ */
+ if (unlikely(file->f_flags & FL_DROP_PRIVS)) {
+ mutex_lock(&inode->i_mutex);
+ file_remove_privs(file);
+ mutex_unlock(&inode->i_mutex);
+ }
+
fsnotify_close(file);
/*
* The function eventpoll_release() should be the first called
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3aa514254161..409bd7047e7e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -913,3 +913,4 @@
#define FL_OFDLCK 1024 /* lock is "owned" by struct file */
#define FL_LAYOUT 2048 /* outstanding pNFS layout */
+#define FL_DROP_PRIVS 4096 /* lest something weird decides that 2 is OK */
diff --git a/mm/memory.c b/mm/memory.c
index c387430f06c3..08a77e0cf65f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2036,6 +2036,7 @@ static inline int wp_page_reuse(struct mm_struct *mm,
if (!page_mkwrite)
file_update_time(vma->vm_file);
+ vma->vm_file->f_flags |= FL_DROP_PRIVS;
}
return VM_FAULT_WRITE;
Willy
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