CVE-2026-99188: net: stmmac: dwmac1000: clear the RGMII status interrupt

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

net: stmmac: dwmac1000: clear the RGMII status interrupt

Since commit 2e2c878a3141 ("net: stmmac: remove SGMII/RGMII/SMII interrupt handling") nothing on the RGMII path reads GMACRGSMIIIS, so RGSMIIIS stays pending behind GMACINTMASK from the first link change on. stmmacresume() resets the MAC in stmmachwsetup(); the reset sets GMACINTMASK to 0 until dwmac1000coreinit() writes the mask again, and the pending status storms the line:

dwmacdmainterrupt: unexpected status 04000000

A register dump at the first message on ODROID-HC4 showed it:

core intstatus 00000001 intmask 00000000 pmt 00000000 rgsmiiis 0000000d

When the resume thread runs on the CPU that takes the MAC interrupt, the storm starves it: a soft lockup, then a watchdog reset or a hang.

Read GMACRGSMIIIS in dwmac1000irqstatus() when the status is not masked, as the driver did before 2e2c878a3141; the read clears it.

Wake-on-LAN resume from s2idle with the resume thread and the MAC interrupt on one CPU: Helios64 (dwmac-rk), 7.3-rc6, soft-locked in 3 of 3 resumes without a fix and in 0 of 10 with this patch; it ran with an out-of-tree dwmac-rk change that keeps the GMAC powered across suspend. ODROID-HC4 (dwmac-meson8b): 0 of 10 with this patch, 2 of 2 without a fix on a 7.3-rc5 build. irqrgmiin went up by one per resume.