CVE-2026-52947

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

net: qrtr: fix refcount saturation and potential UAF in qrtrportremove

In qrtrportremove(), the socket reference count is decremented via __sockput() before the port is removed from the qrtrports XArray and before the RCU grace period elapses.

This breaks the fundamental RCU update paradigm. It exposes a race window where a concurrent RCU reader (such as qrtrresetports() or qrtrportlookup()) can obtain a pointer to the socket from the XArray, and attempt to call sock_hold() on a socket whose reference count has already dropped to zero.

This exact race condition was hit during syzkaller fuzzing, leading to the following refcount saturation warning and a potential Use-After-Free:

refcountt: saturated; leaking memory. WARNING: CPU: 3 PID: 1273 at lib/refcount.c:22 refcountwarnsaturate+0xae/0x1d0 Modules linked in: qrtr(+) bochs drmshmemhelper ... Call Trace: <TASK> qrtrresetports net/qrtr/afqrtr.c:768 [inline] [qrtr] __qrtrbind.isra.0+0x48b/0x570 net/qrtr/afqrtr.c:805 [qrtr] qrtrbind+0x17d/0x210 net/qrtr/afqrtr.c:901 [qrtr] kernelbind+0xe4/0x120 net/socket.c:3592 qrtrnsinit+0x1a6/0x380 net/qrtr/ns.c:715 [qrtr] qrtrprotoinit+0x3b/0xff0 net/qrtr/afqrtr.c:169 [qrtr] dooneinitcall+0xf5/0x5e0 init/main.c:1283 ... </TASK>

Fix this by deferring the reference count decrement until after the xaerase() and the synchronizercu() complete.

(Note: The v1 of this patch incorrectly replaced __sockput() with sockput(). As Simon Horman pointed out, the callers of qrtrportremove() still hold a reference to the socket, so freeing the socket memory here would lead to a subsequent UAF in the caller. Thus, the _sockput() is kept, but only repositioned to close the RCU race.)