CVE-2025-40190

In the Linux kernel, the following vulnerability has been resolved:

ext4: guard against EA inode refcount underflow in xattr update

syzkaller found a path where ext4xattrinodeupdateref() reads an EA inode refcount that is already <= 0 and then applies ref_change (often -1). That lets the refcount underflow and we proceed with a bogus value, triggering errors like:

EXT4-fs error: EA inode <n> ref underflow: refcount=-1 refchange=-1 EXT4-fs warning: ea_inode dec ref err=-117

Make the invariant explicit: if the current refcount is non-positive, treat this as on-disk corruption, emit ext4errorinode(), and fail the operation with -EFSCORRUPTED instead of updating the refcount. Delete the WARNONCE() as negative refcounts are now impossible; keep error reporting in ext4error_inode().

This prevents the underflow and the follow-on orphan/cleanup churn.