Linux Kernel: Infinite loop in handle_tx() for PORT_UNKNOWN
CVE-2026-23472 Published on April 3, 2026
serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN
In the Linux kernel, the following vulnerability has been resolved:
serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN
uart_write_room() and uart_write() behave inconsistently when
xmit_buf is NULL (which happens for PORT_UNKNOWN ports that were
never properly initialized):
- uart_write_room() returns kfifo_avail() which can be > 0
- uart_write() checks xmit_buf and returns 0 if NULL
This inconsistency causes an infinite loop in drivers that rely on
tty_write_room() to determine if they can write:
while (tty_write_room(tty) > 0) {
written = tty->ops->write(...);
// written is always 0, loop never exits
}
For example, caif_serial's handle_tx() enters an infinite loop when
used with PORT_UNKNOWN serial ports, causing system hangs.
Fix by making uart_write_room() also check xmit_buf and return 0 if
it's NULL, consistent with uart_write().
Reproducer: https://gist.github.com/mrpre/d9a694cc0e19828ee3bc3b37983fde13
Products Associated with CVE-2026-23472
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Affected Versions
Linux:- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below efe85a557186b7fe915572ae93a8f3f78bfd9a22 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below bc70f2b36cf474d5cc8ecbcaf57f3e326fdec67c is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 455ce986fa356ff43a43c0d363ba95fa152f21d5 is affected.
- Version 6.18.20, <= 6.18.* is unaffected.
- Version 6.19.10, <= 6.19.* is unaffected.
- Version 7.0-rc5, <= * is unaffected.