From: Cláudio Fernando Pinto The comment above cap_lower(CAP_SYS_RESOURCE) in ovl_fill_super_creds(), added by commit 51f8f3c4e225 ("ovl: drop CAP_SYS_RESOURCE from saved mounter's credentials"), says overlayfs never uses reserved space. Lowering the capability does not stop ext4 from granting its reserved blocks by fsuid: with the default reserve owner and a root mounter, a write through overlayfs still spends them. Say what the code does, without going further. Link: https://lore.kernel.org/linux-unionfs/CAOQ4uxh0g1MtgCO7Q2f4yJP5vq5rLEiiXHbVfeCxwXB5ff4-VQ@mail.gmail.com/ Assisted-by: LLM Signed-off-by: Cláudio Fernando Pinto --- Follow-up to the reserve report after Amir's reply: comment only. --- fs/overlayfs/super.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index bd0a3f9039..21d0cb8719 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -1508,7 +1508,7 @@ static int ovl_fill_super_creds(struct fs_context *fc, struct super_block *sb) else if (!ofs->nofh) sb->s_export_op = &ovl_export_fid_operations; - /* Never override disk quota limits or use reserved space */ + /* Never override disk quota limits or use reserved space by capability */ cap_lower(creator_cred->cap_effective, CAP_SYS_RESOURCE); sb->s_magic = OVERLAYFS_SUPER_MAGIC; --- base-commit: 24a19b953e2a3d0ea5a8c4951a0ab8f32720c907 change-id: 20261019-ovl-comment-3584e63aae25 Best regards, -- Cláudio Fernando Pinto