* UBSAN reports issue in ip_idents_reserve
@ 2016-09-20 12:00 Jiri Pirko
2016-09-20 13:28 ` Eric Dumazet
0 siblings, 1 reply; 14+ messages in thread
From: Jiri Pirko @ 2016-09-20 12:00 UTC (permalink / raw)
To: netdev, eric.dumazet
Hi.
I'm consistently getting following UBSAN warning on every bootup:
[ 47.545820] ================================================================================
[ 47.554340] UBSAN: Undefined behaviour in ./arch/x86/include/asm/atomic.h:156:11
[ 47.561808] signed integer overflow:
[ 47.565420] -2117905507 + -695755206 cannot be represented in type 'int'
[ 47.572226] CPU: 0 PID: 389 Comm: ntpd Not tainted 4.8.0-rc6jiri+ #1
[ 47.578636] Hardware name: Mellanox Technologies Ltd. Mellanox switch/Mellanox switch, BIOS 4.6.5 05/21/2015
[ 47.588586] ffffffff847bf8c0 00000000987b8f47 ffff8803829af5a8 ffffffff818354e3
[ 47.596165] 0000000041b58ab3 ffffffff8277e711 ffffffff81835431 ffff8803829af5d0
[ 47.603722] ffff8803829af580 ffffffffd6879e3a 1ffffffff08f8214 ffffed0070535e6c
[ 47.611298] Call Trace:
[ 47.613795] [<ffffffff818354e3>] dump_stack+0xb2/0x10f
[ 47.619077] [<ffffffff81835431>] ? _atomic_dec_and_lock+0xa1/0xa1
[ 47.625327] [<ffffffff818a884f>] ubsan_epilogue+0xd/0x4e
[ 47.630811] [<ffffffff818a9821>] handle_overflow+0x190/0x1de
[ 47.636627] [<ffffffff818a9691>] ? __ubsan_handle_negate_overflow+0x140/0x140
[ 47.643914] [<ffffffff81863130>] ? iov_iter_copy_from_user_atomic+0x6e0/0x6e0
[ 47.651219] [<ffffffff811e6f79>] ? __lock_acquire.isra.17+0xb79/0xe50
[ 47.657832] [<ffffffff81e581f2>] ? ip_generic_getfrag+0xd2/0x190
[ 47.664011] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320
[ 47.669827] [<ffffffff818a987d>] __ubsan_handle_add_overflow+0xe/0x10
[ 47.676444] [<ffffffff81e41d52>] ip_idents_reserve+0xb2/0xe0
[ 47.682254] [<ffffffff81e443e9>] __ip_select_ident+0x159/0x1b0
[ 47.688248] [<ffffffff81e44290>] ? update_or_create_fnhe+0x850/0x850
[ 47.694782] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320
[ 47.700624] [<ffffffff81e5ef40>] __ip_make_skb+0x8a0/0xab0
[ 47.706259] [<ffffffff81e5f3fd>] ip_make_skb+0x17d/0x1d0
[ 47.711717] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320
[ 47.717526] [<ffffffff81e5f280>] ? ip_flush_pending_frames+0x20/0x20
[ 47.724032] [<ffffffff81e46ef0>] ? ip_rt_update_pmtu+0x4f0/0x4f0
[ 47.730231] [<ffffffff81f35291>] ? xfrm_lookup_route+0x21/0xe0
[ 47.736216] [<ffffffff81ec0cdb>] udp_sendmsg+0x9db/0xf60
[ 47.741668] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320
[ 47.747472] [<ffffffff81ec0300>] ? udp_abort+0x70/0x70
[ 47.752763] [<ffffffff81ede3d8>] inet_sendmsg+0x198/0x220
[ 47.758324] [<ffffffff81ede292>] ? inet_sendmsg+0x52/0x220
[ 47.763982] [<ffffffff81ede240>] ? inet_recvmsg+0x300/0x300
[ 47.769728] [<ffffffff81d6fd25>] sock_sendmsg+0xa5/0xd0
[ 47.775100] [<ffffffff81d72f70>] SYSC_sendto+0x1d0/0x280
[ 47.780551] [<ffffffff81d72da0>] ? SYSC_connect+0x200/0x200
[ 47.786283] [<ffffffff814f66df>] ? poll_select_copy_remaining+0x2af/0x310
[ 47.793265] [<ffffffff814f6430>] ? set_fd_set+0x60/0x60
[ 47.798665] [<ffffffff811ee360>] ? do_raw_spin_trylock+0x90/0x90
[ 47.804853] [<ffffffff814f80e3>] ? SyS_select+0x1a3/0x200
[ 47.810399] [<ffffffff814f7f40>] ? core_sys_select+0x570/0x570
[ 47.816415] [<ffffffff8100467c>] ? exit_to_usermode_loop+0xec/0x110
[ 47.822842] [<ffffffff811e8abd>] ? lockdep_sys_exit+0x2d/0xb0
[ 47.828769] [<ffffffff81004016>] ? lockdep_sys_exit_thunk+0x16/0x30
[ 47.835199] [<ffffffff81d7433e>] SyS_sendto+0xe/0x10
[ 47.840321] [<ffffffff820381f2>] entry_SYSCALL_64_fastpath+0x1a/0xa9
[ 47.846826] ================================================================================
Looks like this might be result of following commit:
commit 04ca6973f7c1a0d8537f2d9906a0cf8e69886d75
Author: Eric Dumazet <edumazet@google.com>
Date: Sat Jul 26 08:58:10 2014 +0200
ip: make IP identifiers less predictable
Eric, could you please take look at that?
Thanks.
Jiri
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: UBSAN reports issue in ip_idents_reserve 2016-09-20 12:00 UBSAN reports issue in ip_idents_reserve Jiri Pirko @ 2016-09-20 13:28 ` Eric Dumazet 2016-09-20 13:36 ` David Laight ` (2 more replies) 0 siblings, 3 replies; 14+ messages in thread From: Eric Dumazet @ 2016-09-20 13:28 UTC (permalink / raw) To: Jiri Pirko; +Cc: netdev On Tue, 2016-09-20 at 14:00 +0200, Jiri Pirko wrote: > Hi. > > I'm consistently getting following UBSAN warning on every bootup: > > [ 47.545820] ================================================================================ > [ 47.554340] UBSAN: Undefined behaviour in ./arch/x86/include/asm/atomic.h:156:11 > [ 47.561808] signed integer overflow: > [ 47.565420] -2117905507 + -695755206 cannot be represented in type 'int' > [ 47.572226] CPU: 0 PID: 389 Comm: ntpd Not tainted 4.8.0-rc6jiri+ #1 > [ 47.578636] Hardware name: Mellanox Technologies Ltd. Mellanox switch/Mellanox switch, BIOS 4.6.5 05/21/2015 > [ 47.588586] ffffffff847bf8c0 00000000987b8f47 ffff8803829af5a8 ffffffff818354e3 > [ 47.596165] 0000000041b58ab3 ffffffff8277e711 ffffffff81835431 ffff8803829af5d0 > [ 47.603722] ffff8803829af580 ffffffffd6879e3a 1ffffffff08f8214 ffffed0070535e6c > [ 47.611298] Call Trace: > [ 47.613795] [<ffffffff818354e3>] dump_stack+0xb2/0x10f > [ 47.619077] [<ffffffff81835431>] ? _atomic_dec_and_lock+0xa1/0xa1 > [ 47.625327] [<ffffffff818a884f>] ubsan_epilogue+0xd/0x4e > [ 47.630811] [<ffffffff818a9821>] handle_overflow+0x190/0x1de > [ 47.636627] [<ffffffff818a9691>] ? __ubsan_handle_negate_overflow+0x140/0x140 > [ 47.643914] [<ffffffff81863130>] ? iov_iter_copy_from_user_atomic+0x6e0/0x6e0 > [ 47.651219] [<ffffffff811e6f79>] ? __lock_acquire.isra.17+0xb79/0xe50 > [ 47.657832] [<ffffffff81e581f2>] ? ip_generic_getfrag+0xd2/0x190 > [ 47.664011] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320 > [ 47.669827] [<ffffffff818a987d>] __ubsan_handle_add_overflow+0xe/0x10 > [ 47.676444] [<ffffffff81e41d52>] ip_idents_reserve+0xb2/0xe0 > [ 47.682254] [<ffffffff81e443e9>] __ip_select_ident+0x159/0x1b0 > [ 47.688248] [<ffffffff81e44290>] ? update_or_create_fnhe+0x850/0x850 > [ 47.694782] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320 > [ 47.700624] [<ffffffff81e5ef40>] __ip_make_skb+0x8a0/0xab0 > [ 47.706259] [<ffffffff81e5f3fd>] ip_make_skb+0x17d/0x1d0 > [ 47.711717] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320 > [ 47.717526] [<ffffffff81e5f280>] ? ip_flush_pending_frames+0x20/0x20 > [ 47.724032] [<ffffffff81e46ef0>] ? ip_rt_update_pmtu+0x4f0/0x4f0 > [ 47.730231] [<ffffffff81f35291>] ? xfrm_lookup_route+0x21/0xe0 > [ 47.736216] [<ffffffff81ec0cdb>] udp_sendmsg+0x9db/0xf60 > [ 47.741668] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320 > [ 47.747472] [<ffffffff81ec0300>] ? udp_abort+0x70/0x70 > [ 47.752763] [<ffffffff81ede3d8>] inet_sendmsg+0x198/0x220 > [ 47.758324] [<ffffffff81ede292>] ? inet_sendmsg+0x52/0x220 > [ 47.763982] [<ffffffff81ede240>] ? inet_recvmsg+0x300/0x300 > [ 47.769728] [<ffffffff81d6fd25>] sock_sendmsg+0xa5/0xd0 > [ 47.775100] [<ffffffff81d72f70>] SYSC_sendto+0x1d0/0x280 > [ 47.780551] [<ffffffff81d72da0>] ? SYSC_connect+0x200/0x200 > [ 47.786283] [<ffffffff814f66df>] ? poll_select_copy_remaining+0x2af/0x310 > [ 47.793265] [<ffffffff814f6430>] ? set_fd_set+0x60/0x60 > [ 47.798665] [<ffffffff811ee360>] ? do_raw_spin_trylock+0x90/0x90 > [ 47.804853] [<ffffffff814f80e3>] ? SyS_select+0x1a3/0x200 > [ 47.810399] [<ffffffff814f7f40>] ? core_sys_select+0x570/0x570 > [ 47.816415] [<ffffffff8100467c>] ? exit_to_usermode_loop+0xec/0x110 > [ 47.822842] [<ffffffff811e8abd>] ? lockdep_sys_exit+0x2d/0xb0 > [ 47.828769] [<ffffffff81004016>] ? lockdep_sys_exit_thunk+0x16/0x30 > [ 47.835199] [<ffffffff81d7433e>] SyS_sendto+0xe/0x10 > [ 47.840321] [<ffffffff820381f2>] entry_SYSCALL_64_fastpath+0x1a/0xa9 > [ 47.846826] ================================================================================ > > Looks like this might be result of following commit: > > commit 04ca6973f7c1a0d8537f2d9906a0cf8e69886d75 > Author: Eric Dumazet <edumazet@google.com> > Date: Sat Jul 26 08:58:10 2014 +0200 > > ip: make IP identifiers less predictable > > Eric, could you please take look at that? Sure I do not think we have to worry here. These is best effort, and unfortunately atomic_t are int. Adding uatomic_t helpers in the kernel with unsigned int would be a huge effort, given this would touch all arches. ^ permalink raw reply [flat|nested] 14+ messages in thread
* RE: UBSAN reports issue in ip_idents_reserve 2016-09-20 13:28 ` Eric Dumazet @ 2016-09-20 13:36 ` David Laight 2016-09-20 13:45 ` Eric Dumazet 2016-09-20 13:39 ` Jiri Pirko 2016-09-21 1:06 ` [PATCH net] net: get rid of an signed integer overflow in ip_idents_reserve() Eric Dumazet 2 siblings, 1 reply; 14+ messages in thread From: David Laight @ 2016-09-20 13:36 UTC (permalink / raw) To: 'Eric Dumazet', Jiri Pirko; +Cc: netdev@vger.kernel.org From: Eric Dumazet > Sent: 20 September 2016 14:29 ... > > [ 47.565420] -2117905507 + -695755206 cannot be represented in type 'int' ... > I do not think we have to worry here. > > These is best effort, and unfortunately atomic_t are int. Not until we compile on a cpu where int arithmetic doesn't wrap. While I expect that various other parts of the kernel (and userspace) wouldn't like such cpu, they do exist. David ^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: UBSAN reports issue in ip_idents_reserve 2016-09-20 13:36 ` David Laight @ 2016-09-20 13:45 ` Eric Dumazet 0 siblings, 0 replies; 14+ messages in thread From: Eric Dumazet @ 2016-09-20 13:45 UTC (permalink / raw) To: David Laight; +Cc: Jiri Pirko, netdev@vger.kernel.org On Tue, 2016-09-20 at 13:36 +0000, David Laight wrote: > From: Eric Dumazet > > Sent: 20 September 2016 14:29 > ... > > > [ 47.565420] -2117905507 + -695755206 cannot be represented in type 'int' > ... > > I do not think we have to worry here. > > > > These is best effort, and unfortunately atomic_t are int. > > Not until we compile on a cpu where int arithmetic doesn't wrap. Then I guess the guy adding this kind of arches in the kernel will have to add all the core kernel infra. If you have an idea, I will happily review a patch. ^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: UBSAN reports issue in ip_idents_reserve 2016-09-20 13:28 ` Eric Dumazet 2016-09-20 13:36 ` David Laight @ 2016-09-20 13:39 ` Jiri Pirko 2016-09-20 14:11 ` Eric Dumazet 2016-09-21 1:06 ` [PATCH net] net: get rid of an signed integer overflow in ip_idents_reserve() Eric Dumazet 2 siblings, 1 reply; 14+ messages in thread From: Jiri Pirko @ 2016-09-20 13:39 UTC (permalink / raw) To: Eric Dumazet; +Cc: netdev Tue, Sep 20, 2016 at 03:28:35PM CEST, eric.dumazet@gmail.com wrote: >On Tue, 2016-09-20 at 14:00 +0200, Jiri Pirko wrote: >> Hi. >> >> I'm consistently getting following UBSAN warning on every bootup: >> >> [ 47.545820] ================================================================================ >> [ 47.554340] UBSAN: Undefined behaviour in ./arch/x86/include/asm/atomic.h:156:11 >> [ 47.561808] signed integer overflow: >> [ 47.565420] -2117905507 + -695755206 cannot be represented in type 'int' >> [ 47.572226] CPU: 0 PID: 389 Comm: ntpd Not tainted 4.8.0-rc6jiri+ #1 >> [ 47.578636] Hardware name: Mellanox Technologies Ltd. Mellanox switch/Mellanox switch, BIOS 4.6.5 05/21/2015 >> [ 47.588586] ffffffff847bf8c0 00000000987b8f47 ffff8803829af5a8 ffffffff818354e3 >> [ 47.596165] 0000000041b58ab3 ffffffff8277e711 ffffffff81835431 ffff8803829af5d0 >> [ 47.603722] ffff8803829af580 ffffffffd6879e3a 1ffffffff08f8214 ffffed0070535e6c >> [ 47.611298] Call Trace: >> [ 47.613795] [<ffffffff818354e3>] dump_stack+0xb2/0x10f >> [ 47.619077] [<ffffffff81835431>] ? _atomic_dec_and_lock+0xa1/0xa1 >> [ 47.625327] [<ffffffff818a884f>] ubsan_epilogue+0xd/0x4e >> [ 47.630811] [<ffffffff818a9821>] handle_overflow+0x190/0x1de >> [ 47.636627] [<ffffffff818a9691>] ? __ubsan_handle_negate_overflow+0x140/0x140 >> [ 47.643914] [<ffffffff81863130>] ? iov_iter_copy_from_user_atomic+0x6e0/0x6e0 >> [ 47.651219] [<ffffffff811e6f79>] ? __lock_acquire.isra.17+0xb79/0xe50 >> [ 47.657832] [<ffffffff81e581f2>] ? ip_generic_getfrag+0xd2/0x190 >> [ 47.664011] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320 >> [ 47.669827] [<ffffffff818a987d>] __ubsan_handle_add_overflow+0xe/0x10 >> [ 47.676444] [<ffffffff81e41d52>] ip_idents_reserve+0xb2/0xe0 >> [ 47.682254] [<ffffffff81e443e9>] __ip_select_ident+0x159/0x1b0 >> [ 47.688248] [<ffffffff81e44290>] ? update_or_create_fnhe+0x850/0x850 >> [ 47.694782] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320 >> [ 47.700624] [<ffffffff81e5ef40>] __ip_make_skb+0x8a0/0xab0 >> [ 47.706259] [<ffffffff81e5f3fd>] ip_make_skb+0x17d/0x1d0 >> [ 47.711717] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320 >> [ 47.717526] [<ffffffff81e5f280>] ? ip_flush_pending_frames+0x20/0x20 >> [ 47.724032] [<ffffffff81e46ef0>] ? ip_rt_update_pmtu+0x4f0/0x4f0 >> [ 47.730231] [<ffffffff81f35291>] ? xfrm_lookup_route+0x21/0xe0 >> [ 47.736216] [<ffffffff81ec0cdb>] udp_sendmsg+0x9db/0xf60 >> [ 47.741668] [<ffffffff81e58120>] ? ip_setup_cork+0x320/0x320 >> [ 47.747472] [<ffffffff81ec0300>] ? udp_abort+0x70/0x70 >> [ 47.752763] [<ffffffff81ede3d8>] inet_sendmsg+0x198/0x220 >> [ 47.758324] [<ffffffff81ede292>] ? inet_sendmsg+0x52/0x220 >> [ 47.763982] [<ffffffff81ede240>] ? inet_recvmsg+0x300/0x300 >> [ 47.769728] [<ffffffff81d6fd25>] sock_sendmsg+0xa5/0xd0 >> [ 47.775100] [<ffffffff81d72f70>] SYSC_sendto+0x1d0/0x280 >> [ 47.780551] [<ffffffff81d72da0>] ? SYSC_connect+0x200/0x200 >> [ 47.786283] [<ffffffff814f66df>] ? poll_select_copy_remaining+0x2af/0x310 >> [ 47.793265] [<ffffffff814f6430>] ? set_fd_set+0x60/0x60 >> [ 47.798665] [<ffffffff811ee360>] ? do_raw_spin_trylock+0x90/0x90 >> [ 47.804853] [<ffffffff814f80e3>] ? SyS_select+0x1a3/0x200 >> [ 47.810399] [<ffffffff814f7f40>] ? core_sys_select+0x570/0x570 >> [ 47.816415] [<ffffffff8100467c>] ? exit_to_usermode_loop+0xec/0x110 >> [ 47.822842] [<ffffffff811e8abd>] ? lockdep_sys_exit+0x2d/0xb0 >> [ 47.828769] [<ffffffff81004016>] ? lockdep_sys_exit_thunk+0x16/0x30 >> [ 47.835199] [<ffffffff81d7433e>] SyS_sendto+0xe/0x10 >> [ 47.840321] [<ffffffff820381f2>] entry_SYSCALL_64_fastpath+0x1a/0xa9 >> [ 47.846826] ================================================================================ >> >> Looks like this might be result of following commit: >> >> commit 04ca6973f7c1a0d8537f2d9906a0cf8e69886d75 >> Author: Eric Dumazet <edumazet@google.com> >> Date: Sat Jul 26 08:58:10 2014 +0200 >> >> ip: make IP identifiers less predictable >> >> Eric, could you please take look at that? > >Sure > >I do not think we have to worry here. > >These is best effort, and unfortunately atomic_t are int. I see. So how to silent the warning? > >Adding uatomic_t helpers in the kernel with unsigned int would be a huge >effort, given this would touch all arches. > > > ^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: UBSAN reports issue in ip_idents_reserve 2016-09-20 13:39 ` Jiri Pirko @ 2016-09-20 14:11 ` Eric Dumazet 2016-09-20 14:18 ` Eric Dumazet 2016-09-20 15:25 ` Eric Dumazet 0 siblings, 2 replies; 14+ messages in thread From: Eric Dumazet @ 2016-09-20 14:11 UTC (permalink / raw) To: Jiri Pirko; +Cc: netdev On Tue, 2016-09-20 at 15:39 +0200, Jiri Pirko wrote: > I see. So how to silent the warning? > We can replace the atomic_add_return() and use a loop around atomic_read() and atomic_cmpxhg() This would change the nice property of x86 xadd into a loop. Or we also could fallback to random generation if the atomic_cmpxchg() fails. I'll provide a patch, thanks. ^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: UBSAN reports issue in ip_idents_reserve 2016-09-20 14:11 ` Eric Dumazet @ 2016-09-20 14:18 ` Eric Dumazet 2016-09-20 14:24 ` Eric Dumazet 2016-09-20 17:46 ` Jiri Pirko 2016-09-20 15:25 ` Eric Dumazet 1 sibling, 2 replies; 14+ messages in thread From: Eric Dumazet @ 2016-09-20 14:18 UTC (permalink / raw) To: Jiri Pirko; +Cc: netdev On Tue, 2016-09-20 at 07:11 -0700, Eric Dumazet wrote: > On Tue, 2016-09-20 at 15:39 +0200, Jiri Pirko wrote: > > > I see. So how to silent the warning? > > > > We can replace the atomic_add_return() and use a loop around > atomic_read() and atomic_cmpxhg() > > This would change the nice property of x86 xadd into a loop. > > Or we also could fallback to random generation if the atomic_cmpxchg() > fails. > > I'll provide a patch, thanks. > Could you try the following ? diff --git a/net/ipv4/route.c b/net/ipv4/route.c index b52496fd51075821c39435f50ac62f813967aecc..91dc108ef6dc75df80f0e73b6fa062d98dc9a58a 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -476,12 +476,19 @@ u32 ip_idents_reserve(u32 hash, int segs) atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; u32 old = ACCESS_ONCE(*p_tstamp); u32 now = (u32)jiffies; - u32 delta = 0; + u32 new, delta = 0; if (old != now && cmpxchg(p_tstamp, old, now) == old) delta = prandom_u32_max(now - old); - return atomic_add_return(segs + delta, p_id) - segs; + old = (u32)atomic_read(p_id); + new = old + delta + segs; + /* Do not try too hard, if multiple cpus are there, + * just fallback to pseudo random number. + */ + if (unlikely(atomic_cmpxchg(p_id, old, new) != old)) + new = prandom_u32(); + return new; } EXPORT_SYMBOL(ip_idents_reserve); ^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: UBSAN reports issue in ip_idents_reserve 2016-09-20 14:18 ` Eric Dumazet @ 2016-09-20 14:24 ` Eric Dumazet 2016-09-20 17:46 ` Jiri Pirko 1 sibling, 0 replies; 14+ messages in thread From: Eric Dumazet @ 2016-09-20 14:24 UTC (permalink / raw) To: Jiri Pirko; +Cc: netdev On Tue, 2016-09-20 at 07:18 -0700, Eric Dumazet wrote: > + */ > + if (unlikely(atomic_cmpxchg(p_id, old, new) != old)) > + new = prandom_u32(); > + return new; Looks like we should return new - segs; ^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: UBSAN reports issue in ip_idents_reserve 2016-09-20 14:18 ` Eric Dumazet 2016-09-20 14:24 ` Eric Dumazet @ 2016-09-20 17:46 ` Jiri Pirko 2016-09-20 18:42 ` Eric Dumazet 1 sibling, 1 reply; 14+ messages in thread From: Jiri Pirko @ 2016-09-20 17:46 UTC (permalink / raw) To: Eric Dumazet; +Cc: netdev Tue, Sep 20, 2016 at 04:18:12PM CEST, eric.dumazet@gmail.com wrote: >On Tue, 2016-09-20 at 07:11 -0700, Eric Dumazet wrote: >> On Tue, 2016-09-20 at 15:39 +0200, Jiri Pirko wrote: >> >> > I see. So how to silent the warning? >> > >> >> We can replace the atomic_add_return() and use a loop around >> atomic_read() and atomic_cmpxhg() >> >> This would change the nice property of x86 xadd into a loop. >> >> Or we also could fallback to random generation if the atomic_cmpxchg() >> fails. >> >> I'll provide a patch, thanks. >> > >Could you try the following ? > >diff --git a/net/ipv4/route.c b/net/ipv4/route.c >index >b52496fd51075821c39435f50ac62f813967aecc..91dc108ef6dc75df80f0e73b6fa062d98dc9a58a 100644 >--- a/net/ipv4/route.c >+++ b/net/ipv4/route.c >@@ -476,12 +476,19 @@ u32 ip_idents_reserve(u32 hash, int segs) > atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; > u32 old = ACCESS_ONCE(*p_tstamp); > u32 now = (u32)jiffies; >- u32 delta = 0; >+ u32 new, delta = 0; > > if (old != now && cmpxchg(p_tstamp, old, now) == old) > delta = prandom_u32_max(now - old); > >- return atomic_add_return(segs + delta, p_id) - segs; >+ old = (u32)atomic_read(p_id); >+ new = old + delta + segs; >+ /* Do not try too hard, if multiple cpus are there, >+ * just fallback to pseudo random number. >+ */ >+ if (unlikely(atomic_cmpxchg(p_id, old, new) != old)) >+ new = prandom_u32(); >+ return new; > } > EXPORT_SYMBOL(ip_idents_reserve); > This patch makes ubsan silent. > > ^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: UBSAN reports issue in ip_idents_reserve 2016-09-20 17:46 ` Jiri Pirko @ 2016-09-20 18:42 ` Eric Dumazet 0 siblings, 0 replies; 14+ messages in thread From: Eric Dumazet @ 2016-09-20 18:42 UTC (permalink / raw) To: Jiri Pirko; +Cc: netdev On Tue, 2016-09-20 at 19:46 +0200, Jiri Pirko wrote: > > This patch makes ubsan silent. Thanks Jiri, I will post an official patch then ;) ^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: UBSAN reports issue in ip_idents_reserve 2016-09-20 14:11 ` Eric Dumazet 2016-09-20 14:18 ` Eric Dumazet @ 2016-09-20 15:25 ` Eric Dumazet 2016-09-20 16:25 ` Jiri Pirko 1 sibling, 1 reply; 14+ messages in thread From: Eric Dumazet @ 2016-09-20 15:25 UTC (permalink / raw) To: Jiri Pirko; +Cc: netdev On Tue, 2016-09-20 at 07:11 -0700, Eric Dumazet wrote: > On Tue, 2016-09-20 at 15:39 +0200, Jiri Pirko wrote: > > > I see. So how to silent the warning? > > > > We can replace the atomic_add_return() and use a loop around > atomic_read() and atomic_cmpxhg() > > This would change the nice property of x86 xadd into a loop. > > Or we also could fallback to random generation if the atomic_cmpxchg() > fails. > > I'll provide a patch, thanks. > I looks at other places, I am surprised you do not see other UBSAN issues in networking :) netdev_refcnt_read() can potentially gives errors as well. ^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: UBSAN reports issue in ip_idents_reserve 2016-09-20 15:25 ` Eric Dumazet @ 2016-09-20 16:25 ` Jiri Pirko 0 siblings, 0 replies; 14+ messages in thread From: Jiri Pirko @ 2016-09-20 16:25 UTC (permalink / raw) To: Eric Dumazet; +Cc: netdev Tue, Sep 20, 2016 at 05:25:16PM CEST, eric.dumazet@gmail.com wrote: >On Tue, 2016-09-20 at 07:11 -0700, Eric Dumazet wrote: >> On Tue, 2016-09-20 at 15:39 +0200, Jiri Pirko wrote: >> >> > I see. So how to silent the warning? >> > >> >> We can replace the atomic_add_return() and use a loop around >> atomic_read() and atomic_cmpxhg() >> >> This would change the nice property of x86 xadd into a loop. >> >> Or we also could fallback to random generation if the atomic_cmpxchg() >> fails. >> >> I'll provide a patch, thanks. >> I'm going to test your patch now. > >I looks at other places, I am surprised you do not see other UBSAN >issues in networking :) Not yet :) > >netdev_refcnt_read() can potentially gives errors as well. > > > ^ permalink raw reply [flat|nested] 14+ messages in thread
* [PATCH net] net: get rid of an signed integer overflow in ip_idents_reserve() 2016-09-20 13:28 ` Eric Dumazet 2016-09-20 13:36 ` David Laight 2016-09-20 13:39 ` Jiri Pirko @ 2016-09-21 1:06 ` Eric Dumazet 2016-09-22 6:42 ` David Miller 2 siblings, 1 reply; 14+ messages in thread From: Eric Dumazet @ 2016-09-21 1:06 UTC (permalink / raw) To: Jiri Pirko, David Miller; +Cc: netdev From: Eric Dumazet <edumazet@google.com> Jiri Pirko reported an UBSAN warning happening in ip_idents_reserve() [] UBSAN: Undefined behaviour in ./arch/x86/include/asm/atomic.h:156:11 [] signed integer overflow: [] -2117905507 + -695755206 cannot be represented in type 'int' Since we do not have uatomic_add_return() yet, use atomic_cmpxchg() so that the arithmetics can be done using unsigned int. Fixes: 04ca6973f7c1 ("ip: make IP identifiers less predictable") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Jiri Pirko <jiri@resnulli.us> --- David, Jiri, I removed the prandom_u32() stuff in favor of a traditional loop to meet stable requirements. Thanks ! net/ipv4/route.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index b52496fd51075821c39435f50ac62f813967aecc..654a9af201366887652a4e19a6f1261e5e747056 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -476,12 +476,18 @@ u32 ip_idents_reserve(u32 hash, int segs) atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; u32 old = ACCESS_ONCE(*p_tstamp); u32 now = (u32)jiffies; - u32 delta = 0; + u32 new, delta = 0; if (old != now && cmpxchg(p_tstamp, old, now) == old) delta = prandom_u32_max(now - old); - return atomic_add_return(segs + delta, p_id) - segs; + /* Do not use atomic_add_return() as it makes UBSAN unhappy */ + do { + old = (u32)atomic_read(p_id); + new = old + delta + segs; + } while (atomic_cmpxchg(p_id, old, new) != old); + + return new - segs; } EXPORT_SYMBOL(ip_idents_reserve); ^ permalink raw reply related [flat|nested] 14+ messages in thread
* Re: [PATCH net] net: get rid of an signed integer overflow in ip_idents_reserve() 2016-09-21 1:06 ` [PATCH net] net: get rid of an signed integer overflow in ip_idents_reserve() Eric Dumazet @ 2016-09-22 6:42 ` David Miller 0 siblings, 0 replies; 14+ messages in thread From: David Miller @ 2016-09-22 6:42 UTC (permalink / raw) To: eric.dumazet; +Cc: jiri, netdev From: Eric Dumazet <eric.dumazet@gmail.com> Date: Tue, 20 Sep 2016 18:06:17 -0700 > From: Eric Dumazet <edumazet@google.com> > > Jiri Pirko reported an UBSAN warning happening in ip_idents_reserve() > > [] UBSAN: Undefined behaviour in ./arch/x86/include/asm/atomic.h:156:11 > [] signed integer overflow: > [] -2117905507 + -695755206 cannot be represented in type 'int' > > Since we do not have uatomic_add_return() yet, use atomic_cmpxchg() > so that the arithmetics can be done using unsigned int. > > Fixes: 04ca6973f7c1 ("ip: make IP identifiers less predictable") > Signed-off-by: Eric Dumazet <edumazet@google.com> > Reported-by: Jiri Pirko <jiri@resnulli.us> > --- > David, Jiri, I removed the prandom_u32() stuff in favor of a traditional > loop to meet stable requirements. Thanks ! Applied. ^ permalink raw reply [flat|nested] 14+ messages in thread
end of thread, other threads:[~2016-09-22 6:43 UTC | newest] Thread overview: 14+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2016-09-20 12:00 UBSAN reports issue in ip_idents_reserve Jiri Pirko 2016-09-20 13:28 ` Eric Dumazet 2016-09-20 13:36 ` David Laight 2016-09-20 13:45 ` Eric Dumazet 2016-09-20 13:39 ` Jiri Pirko 2016-09-20 14:11 ` Eric Dumazet 2016-09-20 14:18 ` Eric Dumazet 2016-09-20 14:24 ` Eric Dumazet 2016-09-20 17:46 ` Jiri Pirko 2016-09-20 18:42 ` Eric Dumazet 2016-09-20 15:25 ` Eric Dumazet 2016-09-20 16:25 ` Jiri Pirko 2016-09-21 1:06 ` [PATCH net] net: get rid of an signed integer overflow in ip_idents_reserve() Eric Dumazet 2016-09-22 6:42 ` David Miller
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