CVE-2026-52947

Summary

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

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

In qrtr_port_remove(), the socket reference count is decremented via __sock_put() before the port is removed from the qrtr_ports 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 qrtr_reset_ports() or qrtr_port_lookup()) 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:

refcount_t: saturated; leaking memory. WARNING: CPU: 3 PID: 1273 at lib/refcount.c:22 refcount_warn_saturate+0xae/0x1d0 Modules linked in: qrtr(+) bochs drm_shmem_helper … Call Trace: <TASK> qrtr_reset_ports net/qrtr/af_qrtr.c:768 [inline] [qrtr] __qrtr_bind.isra.0+0x48b/0x570 net/qrtr/af_qrtr.c:805 [qrtr] qrtr_bind+0x17d/0x210 net/qrtr/af_qrtr.c:901 [qrtr] kernel_bind+0xe4/0x120 net/socket.c:3592 qrtr_ns_init+0x1a6/0x380 net/qrtr/ns.c:715 [qrtr] qrtr_proto_init+0x3b/0xff0 net/qrtr/af_qrtr.c:169 [qrtr] do_one_initcall+0xf5/0x5e0 init/main.c:1283 … </TASK>

Fix this by deferring the reference count decrement until after the xa_erase() and the synchronize_rcu() complete.

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

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/2aa4c12723fe432e623462a3be42a197a128722b
• https://git.kernel.org/stable/c/03bfa95e452e2b6ccd76a332060ae4feaf5ad84d
• https://git.kernel.org/stable/c/474293d90880622fde9d2430fb0165767090f7b3
• https://git.kernel.org/stable/c/2047c2aa0963bb2872fd722300a15bcb441a4c00
• https://git.kernel.org/stable/c/7de2d447072be3b1a76793f034432338fc9c494b
• https://git.kernel.org/stable/c/ab269990ed58143a92a263be1bee626d82ac03da
• https://git.kernel.org/stable/c/3b20ec8f31e8a6a6782243f473b0abd3463621df
• https://git.kernel.org/stable/c/a2171131ecda1ed61a594a1eb715e75fdad0fef5

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