1 files changed, 40 insertions, 4 deletions

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 50e4407398d8..ddfd93f13cc5 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -144,11 +144,47 @@ static int ovl_release(struct inode *inode, struct file *file)
 
 static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
 {
-        struct inode *realinode = ovl_inode_real(file_inode(file));
+        struct inode *inode = file_inode(file);
+        struct fd real;
+        const struct cred *old_cred;
+        ssize_t ret;
+
+        /*
+         * The two special cases below do not need to involve real fs,
+         * so we can optimizing concurrent callers.
+         */
+        if (offset == 0) {
+                if (whence == SEEK_CUR)
+                        return file->f_pos;
+
+                if (whence == SEEK_SET)
+                        return vfs_setpos(file, 0, 0);
+        }
+
+        ret = ovl_real_fdget(file, &real);
+        if (ret)
+                return ret;
 
-        return generic_file_llseek_size(file, offset, whence,
-                                        realinode->i_sb->s_maxbytes,
-                                        i_size_read(realinode));
+        /*
+         * Overlay file f_pos is the master copy that is preserved
+         * through copy up and modified on read/write, but only real
+         * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
+         * limitations that are more strict than ->s_maxbytes for specific
+         * files, so we use the real file to perform seeks.
+         */
+        inode_lock(inode);
+        real.file->f_pos = file->f_pos;
+
+        old_cred = ovl_override_creds(inode->i_sb);
+        ret = vfs_llseek(real.file, offset, whence);
+        revert_creds(old_cred);
+
+        file->f_pos = real.file->f_pos;
+        inode_unlock(inode);
+
+        fdput(real);
+
+        return ret;
 }
 
 static void ovl_file_accessed(struct file *file)