[PATCH v6 7/7] locks: Disable LOCK_MAND support for MS_SHARELOCK mounts

[Pavel Shilovsky]

Signed-off-by: Pavel Shilovsky 
---
 fs/locks.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/locks.c b/fs/locks.c
index 25c3a49..7d67e0e 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1756,6 +1756,12 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
    	goto out;
    }

+	/* Disable LOCK_MAND support for FS mounted with MS_SHARELOCK */
+	if ((cmd & LOCK_MAND) && IS_SHARELOCK(f.file->f_path.dentry->d_inode)) {
+		error = -EPERM;
+		goto out;
+	}
+
    can_sleep = !(cmd & LOCK_NB);
    cmd &= ~LOCK_NB;
    unlock = (cmd == LOCK_UN);