CVE-2026-23095

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

gue: Fix skb memleak with inner IP protocol 0.

syzbot reported skb memleak below. [0]

The repro generated a GUE packet with its inner protocol 0.

gue_udp_recv() returns -guehdr->proto_ctype for resubmit in ip_protocol_deliver_rcu(), but this only works with non-zero protocol number.

Lets drop such packets.

Note that 0 is a valid number (IPv6 Hop-by-Hop Option).

I think it is not practical to encap HOPOPT in GUE, so once someone starts to complain, we could pass down a resubmit flag pointer to distinguish two zeros from the upper layer:

• no error
• resubmit HOPOPT

[0] BUG: memory leak unreferenced object 0xffff888109695a00 (size 240): comm syz.0.17, pid 6088, jiffies 4294943096 hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ……………. 00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00 .@………….. backtrace (crc a84b336f): kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline] slab_post_alloc_hook mm/slub.c:4958 [inline] slab_alloc_node mm/slub.c:5263 [inline] kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270 __build_skb+0x23/0x60 net/core/skbuff.c:474 build_skb+0x20/0x190 net/core/skbuff.c:490 __tun_build_skb drivers/net/tun.c:1541 [inline] tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636 tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770 tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x45d/0x710 fs/read_write.c:686 ksys_write+0xa7/0x170 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Weakness

The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

Affected Software

Potential Mitigations

• Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
• For example, glibc in Linux provides protection against free of invalid pointers.
• When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391].
• To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.

References

• https://git.kernel.org/stable/c/380a82d36e37db49fd41ecc378c22fd29392e96a
• https://git.kernel.org/stable/c/536f5bbc322eb1e175bdd1ced22b236a951c4d8f
• https://git.kernel.org/stable/c/5437a279804ced8088cabb945dba88a26d828f8c
• https://git.kernel.org/stable/c/886f186328b718400dbf79e1bc8cbcbd710ab766
• https://git.kernel.org/stable/c/9a56796ad258786d3624eef5aefba394fc9bdded
• https://git.kernel.org/stable/c/ce569b389a5c78d64788a5ea94560e17fa574b35
• https://git.kernel.org/stable/c/f87b9b7a618c82e7465e872eb10e14c803871892