Affected: Linux, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP, Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

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

net: mvpp2: Prevent parser TCAM memory corruption

Protect the parser TCAM/SRAM memory, and the cached (shadow) SRAM information, from concurrent modifications.

Both the TCAM and SRAM tables are indirectly accessed by configuring an index register that selects the row to read or write to. This means that operations must be atomic in order to, e.g., avoid spreading writes across multiple rows. Since the shadow SRAM array is used to find free rows in the hardware table, it must also be protected in order to avoid TOCTOU errors where multiple cores allocate the same row.

This issue was detected in a situation where `mvpp2_set_rx_mode()` ran concurrently on two CPUs. In this particular case the MVPP2_PE_MAC_UC_PROMISCUOUS entry was corrupted, causing the classifier unit to drop all incoming unicast - indicated by the `rx_classifier_drops` counter.