CVE-2024-44987

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

ipv6: prevent UAF in ip6_send_skb()

syzbot reported an UAF in ip6_send_skb() [1]

After ip6_local_out() has returned, we no longer can safely dereference rt, unless we hold rcu_read_lock().

A similar issue has been fixed in commit a688caa34beb (ipv6: take rcu lock in rawv6_send_hdrinc())

Another potential issue in ip6_finish_output2() is handled in a separate patch.

[1] BUG: KASAN: slab-use-after-free in ip6_send_skb+0x18d/0x230 net/ipv6/ip6_output.c:1964 Read of size 8 at addr ffff88806dde4858 by task syz.1.380/6530

CPU: 1 UID: 0 PID: 6530 Comm: syz.1.380 Not tainted 6.11.0-rc3-syzkaller-00306-gdf6cbc62cc9b #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024 Call Trace: __dump_stack lib/dump_stack.c:93 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:119 print_address_description mm/kasan/report.c:377 [inline] print_report+0x169/0x550 mm/kasan/report.c:488 kasan_report+0x143/0x180 mm/kasan/report.c:601 ip6_send_skb+0x18d/0x230 net/ipv6/ip6_output.c:1964 rawv6_push_pending_frames+0x75c/0x9e0 net/ipv6/raw.c:588 rawv6_sendmsg+0x19c7/0x23c0 net/ipv6/raw.c:926 sock_sendmsg_nosec net/socket.c:730 [inline] __sock_sendmsg+0x1a6/0x270 net/socket.c:745 sock_write_iter+0x2dd/0x400 net/socket.c:1160 do_iter_readv_writev+0x60a/0x890 vfs_writev+0x37c/0xbb0 fs/read_write.c:971 do_writev+0x1b1/0x350 fs/read_write.c:1018 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f936bf79e79 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f936cd7f038 EFLAGS: 00000246 ORIG_RAX: 0000000000000014 RAX: ffffffffffffffda RBX: 00007f936c115f80 RCX: 00007f936bf79e79 RDX: 0000000000000001 RSI: 0000000020000040 RDI: 0000000000000004 RBP: 00007f936bfe7916 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007f936c115f80 R15: 00007fff2860a7a8

Allocated by task 6530: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3f/0x80 mm/kasan/common.c:68 unpoison_slab_object mm/kasan/common.c:312 [inline] __kasan_slab_alloc+0x66/0x80 mm/kasan/common.c:338 kasan_slab_alloc include/linux/kasan.h:201 [inline] slab_post_alloc_hook mm/slub.c:3988 [inline] slab_alloc_node mm/slub.c:4037 [inline] kmem_cache_alloc_noprof+0x135/0x2a0 mm/slub.c:4044 dst_alloc+0x12b/0x190 net/core/dst.c:89 ip6_blackhole_route+0x59/0x340 net/ipv6/route.c:2670 make_blackhole net/xfrm/xfrm_policy.c:3120 [inline] xfrm_lookup_route+0xd1/0x1c0 net/xfrm/xfrm_policy.c:3313 ip6_dst_lookup_flow+0x13e/0x180 net/ipv6/ip6_output.c:1257 rawv6_sendmsg+0x1283/0x23c0 net/ipv6/raw.c:898 sock_sendmsg_nosec net/socket.c:730 [inline] __sock_sendmsg+0x1a6/0x270 net/socket.c:745 ____sys_sendmsg+0x525/0x7d0 net/socket.c:2597 ___sys_sendmsg net/socket.c:2651 [inline] __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2680 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 45: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3f/0x80 mm/kasan/common.c:68 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:579 poison_slab_object+0xe0/0x150 mm/kasan/common.c:240 __kasan_slab_free+0x37/0x60 mm/kasan/common.c:256 kasan_slab_free include/linux/kasan.h:184 [inline] slab_free_hook mm/slub.c:2252 [inline] slab_free mm/slub.c:4473 [inline] kmem_cache_free+0x145/0x350 mm/slub.c:4548 dst_destroy+0x2ac/0x460 net/core/dst.c:124 rcu_do_batch kernel/rcu/tree.c:2569 [inline] rcu_core+0xafd/0x1830 kernel/rcu/tree. —truncated—

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/24e93695b1239fbe4c31e224372be77f82dab69a
• https://git.kernel.org/stable/c/571567e0277008459750f0728f246086b2659429
• https://git.kernel.org/stable/c/9a3e55afa95ed4ac9eda112d4f918af645d72f25
• https://git.kernel.org/stable/c/af1dde074ee2ed7dd5bdca4e7e8ba17f44e7b011
• https://git.kernel.org/stable/c/cb5880a0de12c7f618d2bdd84e2d985f1e06ed7e
• https://git.kernel.org/stable/c/ce2f6cfab2c637d0bd9762104023a15d0ab7c0a8
• https://git.kernel.org/stable/c/e44bd76dd072756e674f45c5be00153f4ded68b2
• https://git.kernel.org/stable/c/faa389b2fbaaec7fd27a390b4896139f9da662e3