AZL-99569

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

gtp: serialize PDP context updates

PDP contexts can be deleted through GTPCMDDELPDP or while the GTP network device is being unregistered. The latter is serialized by RTNL, but the generic-netlink delete path only holds RCU.

Running both paths concurrently can therefore make both paths delete the same PDP context. The issue was found through static analysis and reproduced on a KASAN-enabled kernel by a simple two-thread program racing GTPCMDDELPDP against RTM_DELLINK:

Oops: general protection fault, probably for non-canonical address KASAN: maybe wild-memory-access in range [0xdead000000000120-0xdead000000000127] RIP: gtpgenldel_pdp+0x1c1/0x420 [gtp] RBP: dead000000000122

The second deletion dereferenced the poisoned hlist pprev pointer.

Serialize gtppdpadd(), gtpgenldelpdp(), and gtpdellink() with a shared mutex. Keep the mutex held until the final use of a PDP context in the NEWPDP path, and keep the RCU read-side section around the complete PDP context use in the DELPDP path.