udf: Fix possible corruption when close races with write

When we close a file, we remove preallocated blocks from it. But this
truncation was not protected by i_mutex and thus it could have raced with a
write through a different fd and cause crashes or even filesystem corruption.

Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/udf/file.c b/fs/udf/file.c
index 7464305..b80cbd7 100644 (file)
--- a/fs/udf/file.c
+++ b/fs/udf/file.c
@@ -193,9 +193,11 @@ int udf_ioctl(struct inode *inode, struct file *filp, unsigned int cmd,
 static int udf_release_file(struct inode *inode, struct file *filp)
 {
        if (filp->f_mode & FMODE_WRITE) {
+               mutex_lock(&inode->i_mutex);
                lock_kernel();
                udf_discard_prealloc(inode);
                unlock_kernel();
+               mutex_unlock(&inode->i_mutex);
        }
        return 0;
 }