exFAT: formatting allows >11 char label but volume fails to mount afterward

[jrmwgr]

Hi,

I am encountering a consistent issue when formatting USB drives as exFAT with mintstick.

Environment

• OS: Debian 12
• Desktop: GNOME (GVFS/UDisks2 stack)

Problem

mintstick allows creating an exFAT filesystem with a volume label longer than 11 characters (up to 15). The formatting process completes successfully.

However, after formatting, the device is not mounted anymore.

Reproduction steps

1. Insert a USB drive
2. Open mintstick
3. Format the device as exFAT
4. Set a volume label longer than 11 characters (e.g. "EXFAT-123-TEST")
5. Start formatting

Result

• Formatting completes without error
• The device is not mounted afterward
• Manual mounting may fail depending on the environment (GVFS/UDisks stack)

Expected behavior

mintstick should enforce a safe maximum label length for exFAT to ensure the device can be mounted after formatting.

Notes

According to Microsoft documentation:
https://learn.microsoft.com/en-us/windows/win32/fileio/exfat-specification#73-volume-label-directory-entry

The maximum volume label length is 11 Unicode characters.

In practice, some tools allow longer labels (up to 15), but this can break compatibility with the mounting stack (e.g. GVFS/UDisks), leading to unusable devices after formatting.

Suggested fix

• Limit exFAT label length to 11 characters
• Or ensure compatibility with the mounting stack before accepting longer labels

This currently leads to a successful format operation that results in a non-mounted (and effectively unusable) device.

Thanks

[jrmwgr]

This issue is not limited to the GVFS/UDisks2 automount stack.

On Debian 12, the problem is also reproducible using the standard mount command. When the exFAT volume label exceeds 11 characters, the filesystem cannot be mounted after formatting.

This confirms that the issue is not only related to the desktop environment, but affects the mount process more generally in this environment.