CVE-2024-26865

In the Linux kernel, the following vulnerability has been resolved: rds:
tcp: Fix use-after-free of net in reqsk_timer_handler(). syzkaller reported
a warning of netns tracker [0] followed by KASAN splat [1] and another ref
tracker warning [1]. syzkaller could not find a repro, but in the log, the
only suspicious sequence was as follows: 18:26:22 executing program 1: r0 =
socket$inet6_mptcp(0xa, 0x1, 0x106) … connect$inet6(r0,
&(0x7f0000000080)={0xa, 0x4001, 0x0, @loopback}, 0x1c) (async) The notable
thing here is 0x4001 in connect(), which is RDS_TCP_PORT. So, the scenario
would be: 1. unshare(CLONE_NEWNET) creates a per netns tcp listener in
rds_tcp_listen_init(). 2. syz-executor connect()s to it and creates a
reqsk. 3. syz-executor exit()s immediately. 4. netns is dismantled. [0] 5.
reqsk timer is fired, and UAF happens while freeing reqsk. [1] 6. listener
is freed after RCU grace period. [2] Basically, reqsk assumes that the
listener guarantees netns safety until all reqsk timers are expired by
holding the listener’s refcount. However, this was not the case for kernel
sockets. Commit 740ea3c4a0b2 (“tcp: Clean up kernel listener’s reqsk in
inet_twsk_purge()”) fixed this issue only for per-netns ehash. Let’s apply
the same fix for the global ehash. [0]: ref_tracker: net
notrefcnt@0000000065449cc3 has 1/1 users at sk_alloc
(./include/net/net_namespace.h:337 net/core/sock.c:2146) inet6_create
(net/ipv6/af_inet6.c:192 net/ipv6/af_inet6.c:119) __sock_create
(net/socket.c:1572) rds_tcp_listen_init (net/rds/tcp_listen.c:279)
rds_tcp_init_net (net/rds/tcp.c:577) ops_init
(net/core/net_namespace.c:137) setup_net (net/core/net_namespace.c:340)
copy_net_ns (net/core/net_namespace.c:497) create_new_namespaces
(kernel/nsproxy.c:110) unshare_nsproxy_namespaces (kernel/nsproxy.c:228
(discriminator 4)) ksys_unshare (kernel/fork.c:3429) __x64_sys_unshare
(kernel/fork.c:3496) do_syscall_64 (arch/x86/entry/common.c:52
arch/x86/entry/common.c:83) entry_SYSCALL_64_after_hwframe
(arch/x86/entry/entry_64.S:129) … WARNING: CPU: 0 PID: 27 at
lib/ref_tracker.c:179 ref_tracker_dir_exit (lib/ref_tracker.c:179) [1]:
BUG: KASAN: slab-use-after-free in inet_csk_reqsk_queue_drop
(./include/net/inet_hashtables.h:180 net/ipv4/inet_connection_sock.c:952
net/ipv4/inet_connection_sock.c:966) Read of size 8 at addr
ffff88801b370400 by task swapper/0/0 Hardware name: QEMU Standard PC
(i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org
04/01/2014 Call Trace: <IRQ> dump_stack_lvl (lib/dump_stack.c:107
(discriminator 1)) print_report (mm/kasan/report.c:378
mm/kasan/report.c:488) kasan_report (mm/kasan/report.c:603)
inet_csk_reqsk_queue_drop (./include/net/inet_hashtables.h:180
net/ipv4/inet_connection_sock.c:952 net/ipv4/inet_connection_sock.c:966)
reqsk_timer_handler (net/ipv4/inet_connection_sock.c:979
net/ipv4/inet_connection_sock.c:1092) call_timer_fn
(./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207
./include/trace/events/timer.h:127 kernel/time/timer.c:1701)
__run_timers.part.0 (kernel/time/timer.c:1752 kernel/time/timer.c:2038)
run_timer_softirq (kernel/time/timer.c:2053) __do_softirq
(./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207
./include/trace/events/irq.h:142 kernel/softirq.c:554) irq_exit_rcu
(kernel/softirq.c:427 kernel/softirq.c:632 kernel/softirq.c:644)
sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1076
(discriminator 14)) </IRQ> Allocated by task 258 on cpu 0 at 83.612050s:
kasan_save_stack (mm/kasan/common.c:48) kasan_save_track
(mm/kasan/common.c:68) __kasan_slab_alloc (mm/kasan/common.c:343)
kmem_cache_alloc (mm/slub.c:3813 mm/slub.c:3860 mm/slub.c:3867) copy_net_ns
(./include/linux/slab.h:701 net/core/net_namespace.c:421
net/core/net_namespace.c:480) create_new_namespaces (kernel/nsproxy.c:110)
unshare_nsproxy_name —truncated—

Notes