From: Chi Zhiling Introduce exfat_chain_advance() to walk a exfat_chain structure by a given step, updating both ->dir and ->size fields atomically. This helper handles both ALLOC_NO_FAT_CHAIN and ALLOC_FAT_CHAIN modes with proper boundary checking. Signed-off-by: Chi Zhiling Tested-by: syzbot@syzkaller.appspotmail.com --- fs/exfat/exfat_fs.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h index 530459ab9acc..1035d20ba563 100644 --- a/fs/exfat/exfat_fs.h +++ b/fs/exfat/exfat_fs.h @@ -552,6 +552,23 @@ int exfat_read_volume_label(struct super_block *sb, int exfat_write_volume_label(struct super_block *sb, struct exfat_uni_name *label); +static inline int exfat_chain_advance(struct super_block *sb, + struct exfat_chain *chain, unsigned int step) +{ + if (chain->size >= step) + chain->size -= step; + else + return -EIO; + + if (exfat_fat_walk(sb, &chain->dir, step, chain->flags)) + return -EIO; + + if (chain->size == 0 && chain->flags == ALLOC_NO_FAT_CHAIN) + chain->dir = EXFAT_EOF_CLUSTER; + + return 0; +} + /* inode.c */ extern const struct inode_operations exfat_file_inode_operations; void exfat_sync_inode(struct inode *inode); -- 2.43.0