[PATCH] exfat: fix overflow in cluster-to-dentry conversion

[PATCH] exfat: fix overflow in cluster-to-dentry conversion

[Yang Wen]

The cluster-to-dentry calculation is performed as u32 and may overflow
and wrap around on large volumes. This can result in an incorrect
max_dentries value, causing readdir to stop early and omit directory
entries.

Cast nr_clusters to u64 before shifting to avoid the overflow.

Signed-off-by: Yang Wen <anmuxixixi@gmail.com>
---
 fs/exfat/dir.c      | 2 +-
 fs/exfat/exfat_fs.h | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index 4fd4ec52b8c0..ce5251ba9589 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -87,7 +87,7 @@ static int exfat_readdir(struct inode *inode, loff_t *cpos, struct exfat_dir_ent
 		exfat_bytes_to_cluster(sbi, i_size_read(inode)), ei->flags);
 
 	dentries_per_clu = sbi->dentries_per_clu;
-	max_dentries = min(MAX_EXFAT_DENTRIES,
+	max_dentries = (unsigned int)min_t(u64, MAX_EXFAT_DENTRIES,
 			exfat_cluster_to_dentries(sbi, sbi->num_clusters));
 
 	clu_offset = exfat_dentries_to_cluster(sbi, dentry);
diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index 1f020b041a3d..fa30ab9d8564 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -487,10 +487,10 @@ static inline u32 exfat_dentries_to_bytes(u32 dentry)
 /*
  * helpers for cluster size to dentry size conversion.
  */
-static inline u32 exfat_cluster_to_dentries(struct exfat_sb_info *sbi,
+static inline u64 exfat_cluster_to_dentries(struct exfat_sb_info *sbi,
 		u32 nr_clusters)
 {
-	return nr_clusters << (sbi->cluster_size_bits - DENTRY_SIZE_BITS);
+	return (u64)nr_clusters << (sbi->cluster_size_bits - DENTRY_SIZE_BITS);
 }
 
 static inline u32 exfat_dentries_to_cluster(struct exfat_sb_info *sbi,
-- 
2.34.1

Re: [PATCH] exfat: fix overflow in cluster-to-dentry conversion

[Yang Wen]

Hi,

A gentle ping on this patch.

When you have time, I’d appreciate any review or feedback.

Thanks!

Re: [PATCH] exfat: fix overflow in cluster-to-dentry conversion

[Namjae Jeon]

On Thu, Aug 6, 2026 at 12:13 AM Yang Wen <anmuxixixi@gmail.com> wrote:
>
> Hi,
Hi Yang,
>
> A gentle ping on this patch.
>
> When you have time, I’d appreciate any review or feedback.
Sorry for missing it:). Looks good to me. I will apply it to #dev.
Thanks!