Commit 3a784504 authored by Yuezhang Mo's avatar Yuezhang Mo Committed by Namjae Jeon
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exfat: fix appending discontinuous clusters to empty file 



Eric Hong found that when using ftruncate to expand an empty file,
exfat_ent_set() will fail if discontinuous clusters are allocated.
The reason is that the empty file does not have a cluster chain,
but exfat_ent_set() attempts to append the newly allocated cluster
to the cluster chain. In addition, exfat_find_last_cluster() only
supports finding the last cluster in a non-empty file.

So this commit adds a check whether the file is empty. If the file
is empty, exfat_find_last_cluster() and exfat_ent_set() are no longer
called as they do not need to be called.

Fixes: f55c096f ("exfat: do not zero the extended part")
Reported-by: default avatarEric Hong <erichong@qnap.com>
Signed-off-by: default avatarYuezhang Mo <Yuezhang.Mo@sony.com>
Signed-off-by: default avatarNamjae Jeon <linkinjeon@kernel.org>
parent c02197fc

fs/exfat/file.c

+22 −15
Original line number Diff line number Diff line
@@ -35,13 +35,18 @@ static int exfat_cont_expand(struct inode *inode, loff_t size) 
	if (new_num_clusters == num_clusters)

		goto out;



	if (num_clusters) {

		exfat_chain_set(&clu, ei->start_clu, num_clusters, ei->flags);

		ret = exfat_find_last_cluster(sb, &clu, &last_clu);

		if (ret)

			return ret;



	clu.dir = (last_clu == EXFAT_EOF_CLUSTER) ?

			EXFAT_EOF_CLUSTER : last_clu + 1;

		clu.dir = last_clu + 1;

	} else {

		last_clu = EXFAT_EOF_CLUSTER;

		clu.dir = EXFAT_EOF_CLUSTER;

	}



	clu.size = 0;

	clu.flags = ei->flags;
@@ -51,17 +56,19 @@ static int exfat_cont_expand(struct inode *inode, loff_t size) 
		return ret;



	/* Append new clusters to chain */

	if (clu.flags != ei->flags) {

		exfat_chain_cont_cluster(sb, ei->start_clu, num_clusters);

		ei->flags = ALLOC_FAT_CHAIN;

	}

	if (num_clusters) {

		if (clu.flags != ei->flags)

			if (exfat_chain_cont_cluster(sb, ei->start_clu, num_clusters))

				goto free_clu;



		if (clu.flags == ALLOC_FAT_CHAIN)

			if (exfat_ent_set(sb, last_clu, clu.dir))

				goto free_clu;



	if (num_clusters == 0)

	} else

		ei->start_clu = clu.dir;



	ei->flags = clu.flags;



out:

	inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));

	/* Expanded range not zeroed, do not update valid_size */