From 7b3b28f07af744f5d09c3467e63da1f75e8c8bdd Mon Sep 17 00:00:00 2001 From: Davide Caratti Date: Tue, 16 Jun 2020 22:25:20 +0200 Subject: [PATCH] net/sched: act_gate: fix NULL dereference in tcf_gate_init() it is possible to see a KASAN use-after-free, immediately followed by a NULL dereference crash, with the following command: # tc action add action gate index 3 cycle-time 100000000ns \ > cycle-time-ext 100000000ns clockid CLOCK_TAI BUG: KASAN: use-after-free in tcf_action_init_1+0x8eb/0x960 Write of size 1 at addr ffff88810a5908bc by task tc/883 CPU: 0 PID: 883 Comm: tc Not tainted 5.7.0+ #188 Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014 Call Trace: dump_stack+0x75/0xa0 print_address_description.constprop.6+0x1a/0x220 kasan_report.cold.9+0x37/0x7c tcf_action_init_1+0x8eb/0x960 tcf_action_init+0x157/0x2a0 tcf_action_add+0xd9/0x2f0 tc_ctl_action+0x2a3/0x39d rtnetlink_rcv_msg+0x5f3/0x920 netlink_rcv_skb+0x120/0x380 netlink_unicast+0x439/0x630 netlink_sendmsg+0x714/0xbf0 sock_sendmsg+0xe2/0x110 ____sys_sendmsg+0x5b4/0x890 ___sys_sendmsg+0xe9/0x160 __sys_sendmsg+0xd3/0x170 do_syscall_64+0x9a/0x370 entry_SYSCALL_64_after_hwframe+0x44/0xa9 [...] KASAN: null-ptr-deref in range [0x0000000000000070-0x0000000000000077] CPU: 0 PID: 883 Comm: tc Tainted: G B 5.7.0+ #188 Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014 RIP: 0010:tcf_action_fill_size+0xa3/0xf0 [....] RSP: 0018:ffff88813a48f250 EFLAGS: 00010212 RAX: dffffc0000000000 RBX: 0000000000000094 RCX: ffffffffa47c3eb6 RDX: 000000000000000e RSI: 0000000000000008 RDI: 0000000000000070 RBP: ffff88810a590800 R08: 0000000000000004 R09: ffffed1027491e03 R10: 0000000000000003 R11: ffffed1027491e03 R12: 0000000000000000 R13: 0000000000000000 R14: dffffc0000000000 R15: ffff88810a590800 FS: 00007f62cae8ce40(0000) GS:ffff888147c00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f62c9d20a10 CR3: 000000013a52a000 CR4: 0000000000340ef0 Call Trace: tcf_action_init+0x172/0x2a0 tcf_action_add+0xd9/0x2f0 tc_ctl_action+0x2a3/0x39d rtnetlink_rcv_msg+0x5f3/0x920 netlink_rcv_skb+0x120/0x380 netlink_unicast+0x439/0x630 netlink_sendmsg+0x714/0xbf0 sock_sendmsg+0xe2/0x110 ____sys_sendmsg+0x5b4/0x890 ___sys_sendmsg+0xe9/0x160 __sys_sendmsg+0xd3/0x170 do_syscall_64+0x9a/0x370 entry_SYSCALL_64_after_hwframe+0x44/0xa9 this is caused by the test on 'cycletime_ext', that is still unassigned when the action is newly created. This makes the action .init() return 0 without calling tcf_idr_insert(), hence the UAF + crash. rework the logic that prevents zero values of cycle-time, as follows: 1) 'tcfg_cycletime_ext' seems to be unused in the action software path, and it was already possible by other means to obtain non-zero cycletime and zero cycletime-ext. So, removing that test should not cause any damage. 2) while at it, we must prevent overwriting configuration data with wrong ones: use a temporary variable for 'tcfg_cycletime', and validate it preserving the original semantic (that allowed computing the cycle time as the sum of all intervals, when not specified by TCA_GATE_CYCLE_TIME). 3) remove the test on 'tcfg_cycletime', no more useful, and avoid returning -EFAULT, which did not seem an appropriate return value for a wrong netlink attribute. v3: fix uninitialized 'cycletime' (thanks to Vladimir Oltean) v2: remove useless 'return;' at the end of void gate_get_start_time() Fixes: a51c328df310 ("net: qos: introduce a gate control flow action") CC: Ivan Vecera Signed-off-by: Davide Caratti Acked-by: Vladimir Oltean Tested-by: Vladimir Oltean Signed-off-by: David S. Miller --- net/sched/act_gate.c | 36 +++++++++++++----------------------- 1 file changed, 13 insertions(+), 23 deletions(-) diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c index 9c628591f452c3..94e560c2f81d92 100644 --- a/net/sched/act_gate.c +++ b/net/sched/act_gate.c @@ -32,7 +32,7 @@ static ktime_t gate_get_time(struct tcf_gate *gact) return KTIME_MAX; } -static int gate_get_start_time(struct tcf_gate *gact, ktime_t *start) +static void gate_get_start_time(struct tcf_gate *gact, ktime_t *start) { struct tcf_gate_params *param = &gact->param; ktime_t now, base, cycle; @@ -43,18 +43,13 @@ static int gate_get_start_time(struct tcf_gate *gact, ktime_t *start) if (ktime_after(base, now)) { *start = base; - return 0; + return; } cycle = param->tcfg_cycletime; - /* cycle time should not be zero */ - if (!cycle) - return -EFAULT; - n = div64_u64(ktime_sub_ns(now, base), cycle); *start = ktime_add_ns(base, (n + 1) * cycle); - return 0; } static void gate_start_timer(struct tcf_gate *gact, ktime_t start) @@ -287,12 +282,12 @@ static int tcf_gate_init(struct net *net, struct nlattr *nla, enum tk_offsets tk_offset = TK_OFFS_TAI; struct nlattr *tb[TCA_GATE_MAX + 1]; struct tcf_chain *goto_ch = NULL; + u64 cycletime = 0, basetime = 0; struct tcf_gate_params *p; s32 clockid = CLOCK_TAI; struct tcf_gate *gact; struct tc_gate *parm; int ret = 0, err; - u64 basetime = 0; u32 gflags = 0; s32 prio = -1; ktime_t start; @@ -375,11 +370,8 @@ static int tcf_gate_init(struct net *net, struct nlattr *nla, spin_lock_bh(&gact->tcf_lock); p = &gact->param; - if (tb[TCA_GATE_CYCLE_TIME]) { - p->tcfg_cycletime = nla_get_u64(tb[TCA_GATE_CYCLE_TIME]); - if (!p->tcfg_cycletime_ext) - goto chain_put; - } + if (tb[TCA_GATE_CYCLE_TIME]) + cycletime = nla_get_u64(tb[TCA_GATE_CYCLE_TIME]); if (tb[TCA_GATE_ENTRY_LIST]) { err = parse_gate_list(tb[TCA_GATE_ENTRY_LIST], p, extack); @@ -387,14 +379,19 @@ static int tcf_gate_init(struct net *net, struct nlattr *nla, goto chain_put; } - if (!p->tcfg_cycletime) { + if (!cycletime) { struct tcfg_gate_entry *entry; ktime_t cycle = 0; list_for_each_entry(entry, &p->entries, list) cycle = ktime_add_ns(cycle, entry->interval); - p->tcfg_cycletime = cycle; + cycletime = cycle; + if (!cycletime) { + err = -EINVAL; + goto chain_put; + } } + p->tcfg_cycletime = cycletime; if (tb[TCA_GATE_CYCLE_TIME_EXT]) p->tcfg_cycletime_ext = @@ -408,14 +405,7 @@ static int tcf_gate_init(struct net *net, struct nlattr *nla, gact->tk_offset = tk_offset; hrtimer_init(&gact->hitimer, clockid, HRTIMER_MODE_ABS_SOFT); gact->hitimer.function = gate_timer_func; - - err = gate_get_start_time(gact, &start); - if (err < 0) { - NL_SET_ERR_MSG(extack, - "Internal error: failed get start time"); - release_entry_list(&p->entries); - goto chain_put; - } + gate_get_start_time(gact, &start); gact->current_close_time = start; gact->current_gate_status = GATE_ACT_GATE_OPEN | GATE_ACT_PENDING;