CVE-2023-52999

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

net: fix UaF in netns ops registration error path

If net_assign_generic() fails, the current error path in ops_init() tries to clear the gen pointer slot. Anyway, in such error path, the gen pointer itself has not been modified yet, and the existing and accessed one is smaller than the accessed index, causing an out-of-bounds error:

BUG: KASAN: slab-out-of-bounds in ops_init+0x2de/0x320 Write of size 8 at addr ffff888109124978 by task modprobe/1018

CPU: 2 PID: 1018 Comm: modprobe Not tainted 6.2.0-rc2.mptcp_ae5ac65fbed5+ #1641 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.1-2.fc37 04/01/2014 Call Trace: dump_stack_lvl+0x6a/0x9f print_address_description.constprop.0+0x86/0x2b5 print_report+0x11b/0x1fb kasan_report+0x87/0xc0 ops_init+0x2de/0x320 register_pernet_operations+0x2e4/0x750 register_pernet_subsys+0x24/0x40 tcf_register_action+0x9f/0x560 do_one_initcall+0xf9/0x570 do_init_module+0x190/0x650 load_module+0x1fa5/0x23c0 __do_sys_finit_module+0x10d/0x1b0 do_syscall_64+0x58/0x80 entry_SYSCALL_64_after_hwframe+0x72/0xdc RIP: 0033:0x7f42518f778d Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d cb 56 2c 00 f7 d8 64 89 01 48 RSP: 002b:00007fff96869688 EFLAGS: 00000246 ORIG_RAX: 0000000000000139 RAX: ffffffffffffffda RBX: 00005568ef7f7c90 RCX: 00007f42518f778d RDX: 0000000000000000 RSI: 00005568ef41d796 RDI: 0000000000000003 RBP: 00005568ef41d796 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000000 R13: 00005568ef7f7d30 R14: 0000000000040000 R15: 0000000000000000

This change addresses the issue by skipping the gen pointer de-reference in the mentioned error-path.

Found by code inspection and verified with explicit error injection on a kasan-enabled kernel.

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• https://git.kernel.org/stable/c/12075708f2e77ee6a9f8bb2cf512c38be3099794
• https://git.kernel.org/stable/c/66689a72ba73575e76d4f6a8748d3fa2690ec1c4
• https://git.kernel.org/stable/c/71ab9c3e2253619136c31c89dbb2c69305cc89b1
• https://git.kernel.org/stable/c/ad0dfe9bcf0d78e699c7efb64c90ed062dc48bea
• https://git.kernel.org/stable/c/d4c008f3b7f7d4ffd311eb2dae5e75b3cbddacd0
• https://git.kernel.org/stable/c/ddd49cbbd4c1ceb38032018b589b44208e54f55e