1 files changed, 72 insertions, 1 deletions

diff --git a/fs/open.c b/fs/open.c
index b47aab39c057..d05e18c60bae 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -890,15 +890,86 @@ void fd_install(unsigned int fd, struct file *file)
 
 EXPORT_SYMBOL(fd_install);
 
+static inline int build_open_flags(int flags, int mode, struct open_flags *op)
+{
+        int lookup_flags = 0;
+        int acc_mode;
+
+        if (!(flags & O_CREAT))
+                mode = 0;
+        op->mode = mode;
+
+        /* Must never be set by userspace */
+        flags &= ~FMODE_NONOTIFY;
+
+        /*
+         * O_SYNC is implemented as __O_SYNC|O_DSYNC.  As many places only
+         * check for O_DSYNC if the need any syncing at all we enforce it's
+         * always set instead of having to deal with possibly weird behaviour
+         * for malicious applications setting only __O_SYNC.
+         */
+        if (flags & __O_SYNC)
+                flags |= O_DSYNC;
+
+        op->open_flag = flags;
+
+        acc_mode = MAY_OPEN | ACC_MODE(flags);
+
+        /* O_TRUNC implies we need access checks for write permissions */
+        if (flags & O_TRUNC)
+                acc_mode |= MAY_WRITE;
+
+        /* Allow the LSM permission hook to distinguish append
+           access from general write access. */
+        if (flags & O_APPEND)
+                acc_mode |= MAY_APPEND;
+
+        op->acc_mode = acc_mode;
+
+        op->intent = LOOKUP_OPEN;
+        if (flags & O_CREAT) {
+                op->intent |= LOOKUP_CREATE;
+                if (flags & O_EXCL)
+                        op->intent |= LOOKUP_EXCL;
+        }
+
+        if (flags & O_DIRECTORY)
+                lookup_flags |= LOOKUP_DIRECTORY;
+        if (!(flags & O_NOFOLLOW))
+                lookup_flags |= LOOKUP_FOLLOW;
+        return lookup_flags;
+}
+
+/**
+ * filp_open - open file and return file pointer
+ *
+ * @filename:   path to open
+ * @flags:      open flags as per the open(2) second argument
+ * @mode:       mode for the new file if O_CREAT is set, else ignored
+ *
+ * This is the helper to open a file from kernelspace if you really
+ * have to.  But in generally you should not do this, so please move
+ * along, nothing to see here..
+ */
+struct file *filp_open(const char *filename, int flags, int mode)
+{
+        struct open_flags op;
+        int lookup = build_open_flags(flags, mode, &op);
+        return do_filp_open(AT_FDCWD, filename, &op, lookup);
+}
+EXPORT_SYMBOL(filp_open);
+
 long do_sys_open(int dfd, const char __user *filename, int flags, int mode)
 {
+        struct open_flags op;
+        int lookup = build_open_flags(flags, mode, &op);
         char *tmp = getname(filename);
         int fd = PTR_ERR(tmp);
 
         if (!IS_ERR(tmp)) {
                 fd = get_unused_fd_flags(flags);
                 if (fd >= 0) {
-                        struct file *f = do_filp_open(dfd, tmp, flags, mode, 0);
+                        struct file *f = do_filp_open(dfd, tmp, &op, lookup);
                         if (IS_ERR(f)) {
                                 put_unused_fd(fd);
                                 fd = PTR_ERR(f);