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>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/udf/file.c b/fs/udf/file.c
index 7464305382b5..b80cbd78833c 100644
--- 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;
 }