CVE-2025-40186 — tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request().

Affected: Linux

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

tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request().

syzbot reported the splat below in tcp_conn_request(). [0]

If a listener is close()d while a TFO socket is being processed in tcp_conn_request(), inet_csk_reqsk_queue_add() does not set reqsk->sk and calls inet_child_forget(), which calls tcp_disconnect() for the TFO socket.

After the cited commit, tcp_disconnect() calls reqsk_fastopen_remove(), where reqsk_put() is called due to !reqsk->sk.

Then, reqsk_fastopen_remove() in tcp_conn_request() decrements the last req->rsk_refcnt and frees reqsk, and __reqsk_free() at the drop_and_free label causes the refcount underflow for the listener and double-free of the reqsk.

Let's remove reqsk_fastopen_remove() in tcp_conn_request().

Note that other callers make sure tp->fastopen_rsk is not NULL.

[0]: refcount_t: underflow; use-after-free. WARNING: CPU: 12 PID: 5563 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28) Modules linked in: CPU: 12 UID: 0 PID: 5563 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:refcount_warn_saturate (lib/refcount.c:28) Code: ab e8 8e b4 98 ff 0f 0b c3 cc cc cc cc cc 80 3d a4 e4 d6 01 00 75 9c c6 05 9b e4 d6 01 01 48 c7 c7 e8 df fb ab e8 6a b4 98 ff <0f> 0b e9 03 5b 76 00 cc 80 3d 7d e4 d6 01 00 0f 85 74 ff ff ff c6 RSP: 0018:ffffa79fc0304a98 EFLAGS…

USN-8029-1 — linux, linux-raspi, linux-realtime vulnerabilities

Affected: Ubuntu:25.10: linux, Ubuntu:25.10: linux-raspi, Ubuntu:25.10: linux-realtime

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - ARM64 architecture; - MIPS architecture; - Nios II architecture; - PA-RISC architecture; - RISC-V architecture; - S390 architecture; - Sun Sparc architecture; - x86 architecture; - Xtensa architecture; - Block layer subsystem; - Cryptographic API; - Compute Acceleration Framework; - ACPI drivers; - Drivers core; - Network block device driver; - Bluetooth drivers; - Bus devices; - Hardware random number generator core; - Character device driver; - Clock framework and drivers; - Data acquisition framework and drivers; - CPU frequency scaling framework; - Hardware crypto device drivers; - CXL (Compute Express Link) drivers; - Device frequency scaling framework; - ARM SCMI message protocol; - GPIO subsystem; - GPU drivers; - Hardware monitoring drivers; - HW tracing; - InfiniBand drivers; - Input Device (Miscellaneous) drivers; - IOMMU subsystem; - ISDN/mISDN subsystem; - Mailbox framework; - Multiple devices driver; - Media drivers; - Fastrpc Driver; - PCI Endpoint Test driver; - VMware Balloon Driver; - MOST (Media Oriented Systems Transport) drivers; - Network drivers; - Mellanox network drivers; - STMicroelectronics network drivers; - NVME drivers; - PCI subsystem; - Performance monitor drivers; - Pin…

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CVE-2025-40186 — tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request().

USN-8029-1 — linux, linux-raspi, linux-realtime vulnerabilities