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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: f55c096f62 ("exfat: do not zero the extended part")
Reported-by: Eric Hong <erichong@qnap.com>
Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
This commit is contained in:
Yuezhang Mo 2024-02-16 20:19:55 +08:00 committed by Namjae Jeon
parent c02197fc90
commit 3a7845041e
1 changed files with 21 additions and 14 deletions
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35
fs/exfat/file.c
View File

@ -35,13 +35,18 @@ static int exfat_cont_expand(struct inode *inode, loff_t size)
if (new_num_clusters == num_clusters)
goto out;
exfat_chain_set(&clu, ei->start_clu, num_clusters, ei->flags);
ret = exfat_find_last_cluster(sb, &clu, &last_clu);
if (ret)
return ret;
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 + 1;
} else {
last_clu = EXFAT_EOF_CLUSTER;
clu.dir = EXFAT_EOF_CLUSTER;
}
clu.dir = (last_clu == EXFAT_EOF_CLUSTER) ?
EXFAT_EOF_CLUSTER : last_clu + 1;
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 (clu.flags == ALLOC_FAT_CHAIN)
if (exfat_ent_set(sb, last_clu, clu.dir))
goto free_clu;
if (num_clusters) {
if (clu.flags != ei->flags)
if (exfat_chain_cont_cluster(sb, ei->start_clu, num_clusters))
goto free_clu;
if (num_clusters == 0)
if (clu.flags == ALLOC_FAT_CHAIN)
if (exfat_ent_set(sb, last_clu, clu.dir))
goto free_clu;
} 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 */