| Message ID | 1402059375.3645.284.camel@edumazet-glaptop2.roam.corp.google.com |
|---|---|
| State | RFC, archived |
| Delegated to: | David Miller |
| Headers | show |
On Fri, Jun 6, 2014 at 5:56 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > On Fri, 2014-06-06 at 15:29 +0400, Alexey Preobrazhensky wrote: >> Hello, >> >> I’m working on AddressSanitizer[1] -- a tool that detects >> use-after-free and out-of-bounds bugs in kernel. >> >> We’ve encountered a heap-use-after-free in ip4_datagram_release_cb() >> in linux kernel 3.15-rc5 (revision >> 60b5f90d0fac7585f1a43ccdad06787b97eda0ab). >> >> It seems to be a race between dst_release() and >> ip4_datagram_release_cb() on an object from ip_dst_cache slab, all >> during the ip4_datagram_connect() call. >> >> This heap-use-after-free was triggered under trinity syscall fuzzer, >> so there is no reproducer. >> >> It would be great if someone familiar with the code took time to look >> into this report. >> >> Thanks, >> Alexey >> >> [1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel >> >> >> AddressSanitizer: heap-use-after-free in ipv4_dst_check >> Read of size 2 by thread T15453: >> [<ffffffff817daa3a>] ipv4_dst_check+0x1a/0x90 ./net/ipv4/route.c:1116 >> [<ffffffff8175b789>] __sk_dst_check+0x89/0xe0 ./net/core/sock.c:531 >> [<ffffffff81830a36>] ip4_datagram_release_cb+0x46/0x390 ??:0 >> [<ffffffff8175eaea>] release_sock+0x17a/0x230 ./net/core/sock.c:2413 >> [<ffffffff81830882>] ip4_datagram_connect+0x462/0x5d0 ??:0 >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534 >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701 >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682 >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b >> ./arch/x86/kernel/entry_64.S:629 >> >> Freed by thread T15455: >> [<ffffffff8178d9b8>] dst_destroy+0xa8/0x160 ./net/core/dst.c:251 >> [<ffffffff8178de25>] dst_release+0x45/0x80 ./net/core/dst.c:280 >> [<ffffffff818304c1>] ip4_datagram_connect+0xa1/0x5d0 ??:0 >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534 >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701 >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682 >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b >> ./arch/x86/kernel/entry_64.S:629 >> >> Allocated by thread T15453: >> [<ffffffff8178d291>] dst_alloc+0x81/0x2b0 ./net/core/dst.c:171 >> [<ffffffff817db3b7>] rt_dst_alloc+0x47/0x50 ./net/ipv4/route.c:1406 >> [< inlined >] __ip_route_output_key+0x3e8/0xf70 >> __mkroute_output ./net/ipv4/route.c:1939 >> [<ffffffff817dde08>] __ip_route_output_key+0x3e8/0xf70 ./net/ipv4/route.c:2161 >> [<ffffffff817deb34>] ip_route_output_flow+0x14/0x30 ./net/ipv4/route.c:2249 >> [<ffffffff81830737>] ip4_datagram_connect+0x317/0x5d0 ??:0 >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534 >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701 >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682 >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b >> ./arch/x86/kernel/entry_64.S:629 >> >> The buggy address ffff880024ff2266 is located 102 bytes inside >> of 192-byte region [ffff880024ff2200, ffff880024ff22c0) >> >> Memory state around the buggy address: >> ffff880024ff1d00: ffffffff fffrrrrr rrrrrrrr rrrrrrrr >> ffff880024ff1e00: ffffffff ffffffff ffffffff fffrrrrr >> ffff880024ff1f00: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr >> ffff880024ff2000: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr >> ffff880024ff2100: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr >> >ffff880024ff2200: ffffffff ffffffff ffffffff rrrrrrrr >> ^ >> ffff880024ff2300: rrrrrrrr rrrrrrrr ........ ........ >> ffff880024ff2400: ........ rrrrrrrr rrrrrrrr rrrrrrrr >> ffff880024ff2500: ffffffff ffffffff ffffffff rrrrrrrr >> ffff880024ff2600: rrrrrrrr rrrrrrrr ffffffff ffffffff >> ffff880024ff2700: ffffffff rrrrrrrr rrrrrrrr rrrrrrrr >> Legend: >> f - 8 freed bytes >> r - 8 redzone bytes >> . - 8 allocated bytes >> x=1..7 - x allocated bytes + (8-x) redzone bytes >> -- > > > Yeah, we had many reports in the past that something was wrong ... > > Your nice report made me take a look, finally :( > > Problem comes from > > net/ipv4/udp.c:1008: sk_dst_set(sk, dst_clone(&rt->dst)); > > Could you try following patch ? > > Thanks ! > > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c > index 4468e1adc094..d5e68ee63b8f 100644 > --- a/net/ipv4/udp.c > +++ b/net/ipv4/udp.c > @@ -1004,8 +1004,11 @@ int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, > if ((rt->rt_flags & RTCF_BROADCAST) && > !sock_flag(sk, SOCK_BROADCAST)) > goto out; > - if (connected) > - sk_dst_set(sk, dst_clone(&rt->dst)); > + if (connected) { > + spin_lock_bh(&sk->sk_lock.slock); > + __sk_dst_set(sk, dst_clone(&rt->dst)); > + spin_unlock_bh(&sk->sk_lock.slock); > + } Nice catch. Should then we change sk_dst_set() itself to do spin_lock_bh unconditionally? Seems overhead is smaller, than checking all possible callsites manually. cc-ing Dormando as well. > } > > if (msg->msg_flags&MSG_CONFIRM) > > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, 2014-06-06 at 08:59 -0700, Alexei Starovoitov wrote: > On Fri, Jun 6, 2014 at 5:56 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > > On Fri, 2014-06-06 at 15:29 +0400, Alexey Preobrazhensky wrote: > >> Hello, > >> > >> I’m working on AddressSanitizer[1] -- a tool that detects > >> use-after-free and out-of-bounds bugs in kernel. > >> > >> We’ve encountered a heap-use-after-free in ip4_datagram_release_cb() > >> in linux kernel 3.15-rc5 (revision > >> 60b5f90d0fac7585f1a43ccdad06787b97eda0ab). > >> > >> It seems to be a race between dst_release() and > >> ip4_datagram_release_cb() on an object from ip_dst_cache slab, all > >> during the ip4_datagram_connect() call. > >> > >> This heap-use-after-free was triggered under trinity syscall fuzzer, > >> so there is no reproducer. > >> > >> It would be great if someone familiar with the code took time to look > >> into this report. > >> > >> Thanks, > >> Alexey > >> > >> [1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel > >> > >> > >> AddressSanitizer: heap-use-after-free in ipv4_dst_check > >> Read of size 2 by thread T15453: > >> [<ffffffff817daa3a>] ipv4_dst_check+0x1a/0x90 ./net/ipv4/route.c:1116 > >> [<ffffffff8175b789>] __sk_dst_check+0x89/0xe0 ./net/core/sock.c:531 > >> [<ffffffff81830a36>] ip4_datagram_release_cb+0x46/0x390 ??:0 > >> [<ffffffff8175eaea>] release_sock+0x17a/0x230 ./net/core/sock.c:2413 > >> [<ffffffff81830882>] ip4_datagram_connect+0x462/0x5d0 ??:0 > >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534 > >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701 > >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682 > >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b > >> ./arch/x86/kernel/entry_64.S:629 > >> > >> Freed by thread T15455: > >> [<ffffffff8178d9b8>] dst_destroy+0xa8/0x160 ./net/core/dst.c:251 > >> [<ffffffff8178de25>] dst_release+0x45/0x80 ./net/core/dst.c:280 > >> [<ffffffff818304c1>] ip4_datagram_connect+0xa1/0x5d0 ??:0 > >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534 > >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701 > >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682 > >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b > >> ./arch/x86/kernel/entry_64.S:629 > >> > >> Allocated by thread T15453: > >> [<ffffffff8178d291>] dst_alloc+0x81/0x2b0 ./net/core/dst.c:171 > >> [<ffffffff817db3b7>] rt_dst_alloc+0x47/0x50 ./net/ipv4/route.c:1406 > >> [< inlined >] __ip_route_output_key+0x3e8/0xf70 > >> __mkroute_output ./net/ipv4/route.c:1939 > >> [<ffffffff817dde08>] __ip_route_output_key+0x3e8/0xf70 ./net/ipv4/route.c:2161 > >> [<ffffffff817deb34>] ip_route_output_flow+0x14/0x30 ./net/ipv4/route.c:2249 > >> [<ffffffff81830737>] ip4_datagram_connect+0x317/0x5d0 ??:0 > >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534 > >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701 > >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682 > >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b > >> ./arch/x86/kernel/entry_64.S:629 > >> > >> The buggy address ffff880024ff2266 is located 102 bytes inside > >> of 192-byte region [ffff880024ff2200, ffff880024ff22c0) > >> > >> Memory state around the buggy address: > >> ffff880024ff1d00: ffffffff fffrrrrr rrrrrrrr rrrrrrrr > >> ffff880024ff1e00: ffffffff ffffffff ffffffff fffrrrrr > >> ffff880024ff1f00: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr > >> ffff880024ff2000: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr > >> ffff880024ff2100: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr > >> >ffff880024ff2200: ffffffff ffffffff ffffffff rrrrrrrr > >> ^ > >> ffff880024ff2300: rrrrrrrr rrrrrrrr ........ ........ > >> ffff880024ff2400: ........ rrrrrrrr rrrrrrrr rrrrrrrr > >> ffff880024ff2500: ffffffff ffffffff ffffffff rrrrrrrr > >> ffff880024ff2600: rrrrrrrr rrrrrrrr ffffffff ffffffff > >> ffff880024ff2700: ffffffff rrrrrrrr rrrrrrrr rrrrrrrr > >> Legend: > >> f - 8 freed bytes > >> r - 8 redzone bytes > >> . - 8 allocated bytes > >> x=1..7 - x allocated bytes + (8-x) redzone bytes > >> -- > > > > > > Yeah, we had many reports in the past that something was wrong ... > > > > Your nice report made me take a look, finally :( > > > > Problem comes from > > > > net/ipv4/udp.c:1008: sk_dst_set(sk, dst_clone(&rt->dst)); > > > > Could you try following patch ? > > > > Thanks ! > > > > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c > > index 4468e1adc094..d5e68ee63b8f 100644 > > --- a/net/ipv4/udp.c > > +++ b/net/ipv4/udp.c > > @@ -1004,8 +1004,11 @@ int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, > > if ((rt->rt_flags & RTCF_BROADCAST) && > > !sock_flag(sk, SOCK_BROADCAST)) > > goto out; > > - if (connected) > > - sk_dst_set(sk, dst_clone(&rt->dst)); > > + if (connected) { > > + spin_lock_bh(&sk->sk_lock.slock); > > + __sk_dst_set(sk, dst_clone(&rt->dst)); > > + spin_unlock_bh(&sk->sk_lock.slock); > > + } > > Nice catch. > Should then we change sk_dst_set() itself to do spin_lock_bh unconditionally? > Seems overhead is smaller, than checking all possible callsites manually. > > cc-ing Dormando as well. Real problem is that sk_dst_set() uses a different lock. I never understood how this was supposed to work. We should either : 1) use xchg() and no lock at all to change sk_dst_cache, as we did for sk_rx_dst ( cf udp_sk_rx_dst_set() ) 2) No longer use sk_dst_lock, and always use the socket lock (sk->sk_lock.slock) instead. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Jun 6, 2014 at 9:16 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > On Fri, 2014-06-06 at 08:59 -0700, Alexei Starovoitov wrote: >> On Fri, Jun 6, 2014 at 5:56 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: >> > On Fri, 2014-06-06 at 15:29 +0400, Alexey Preobrazhensky wrote: >> >> Hello, >> >> >> >> I’m working on AddressSanitizer[1] -- a tool that detects >> >> use-after-free and out-of-bounds bugs in kernel. >> >> >> >> We’ve encountered a heap-use-after-free in ip4_datagram_release_cb() >> >> in linux kernel 3.15-rc5 (revision >> >> 60b5f90d0fac7585f1a43ccdad06787b97eda0ab). >> >> >> >> It seems to be a race between dst_release() and >> >> ip4_datagram_release_cb() on an object from ip_dst_cache slab, all >> >> during the ip4_datagram_connect() call. >> >> >> >> This heap-use-after-free was triggered under trinity syscall fuzzer, >> >> so there is no reproducer. >> >> >> >> It would be great if someone familiar with the code took time to look >> >> into this report. >> >> >> >> Thanks, >> >> Alexey >> >> >> >> [1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel >> >> >> >> >> >> AddressSanitizer: heap-use-after-free in ipv4_dst_check >> >> Read of size 2 by thread T15453: >> >> [<ffffffff817daa3a>] ipv4_dst_check+0x1a/0x90 ./net/ipv4/route.c:1116 >> >> [<ffffffff8175b789>] __sk_dst_check+0x89/0xe0 ./net/core/sock.c:531 >> >> [<ffffffff81830a36>] ip4_datagram_release_cb+0x46/0x390 ??:0 >> >> [<ffffffff8175eaea>] release_sock+0x17a/0x230 ./net/core/sock.c:2413 >> >> [<ffffffff81830882>] ip4_datagram_connect+0x462/0x5d0 ??:0 >> >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534 >> >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701 >> >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682 >> >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b >> >> ./arch/x86/kernel/entry_64.S:629 >> >> >> >> Freed by thread T15455: >> >> [<ffffffff8178d9b8>] dst_destroy+0xa8/0x160 ./net/core/dst.c:251 >> >> [<ffffffff8178de25>] dst_release+0x45/0x80 ./net/core/dst.c:280 >> >> [<ffffffff818304c1>] ip4_datagram_connect+0xa1/0x5d0 ??:0 >> >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534 >> >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701 >> >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682 >> >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b >> >> ./arch/x86/kernel/entry_64.S:629 >> >> >> >> Allocated by thread T15453: >> >> [<ffffffff8178d291>] dst_alloc+0x81/0x2b0 ./net/core/dst.c:171 >> >> [<ffffffff817db3b7>] rt_dst_alloc+0x47/0x50 ./net/ipv4/route.c:1406 >> >> [< inlined >] __ip_route_output_key+0x3e8/0xf70 >> >> __mkroute_output ./net/ipv4/route.c:1939 >> >> [<ffffffff817dde08>] __ip_route_output_key+0x3e8/0xf70 ./net/ipv4/route.c:2161 >> >> [<ffffffff817deb34>] ip_route_output_flow+0x14/0x30 ./net/ipv4/route.c:2249 >> >> [<ffffffff81830737>] ip4_datagram_connect+0x317/0x5d0 ??:0 >> >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534 >> >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701 >> >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682 >> >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b >> >> ./arch/x86/kernel/entry_64.S:629 >> >> >> >> The buggy address ffff880024ff2266 is located 102 bytes inside >> >> of 192-byte region [ffff880024ff2200, ffff880024ff22c0) >> >> >> >> Memory state around the buggy address: >> >> ffff880024ff1d00: ffffffff fffrrrrr rrrrrrrr rrrrrrrr >> >> ffff880024ff1e00: ffffffff ffffffff ffffffff fffrrrrr >> >> ffff880024ff1f00: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr >> >> ffff880024ff2000: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr >> >> ffff880024ff2100: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr >> >> >ffff880024ff2200: ffffffff ffffffff ffffffff rrrrrrrr >> >> ^ >> >> ffff880024ff2300: rrrrrrrr rrrrrrrr ........ ........ >> >> ffff880024ff2400: ........ rrrrrrrr rrrrrrrr rrrrrrrr >> >> ffff880024ff2500: ffffffff ffffffff ffffffff rrrrrrrr >> >> ffff880024ff2600: rrrrrrrr rrrrrrrr ffffffff ffffffff >> >> ffff880024ff2700: ffffffff rrrrrrrr rrrrrrrr rrrrrrrr >> >> Legend: >> >> f - 8 freed bytes >> >> r - 8 redzone bytes >> >> . - 8 allocated bytes >> >> x=1..7 - x allocated bytes + (8-x) redzone bytes >> >> -- >> > >> > >> > Yeah, we had many reports in the past that something was wrong ... >> > >> > Your nice report made me take a look, finally :( >> > >> > Problem comes from >> > >> > net/ipv4/udp.c:1008: sk_dst_set(sk, dst_clone(&rt->dst)); >> > >> > Could you try following patch ? >> > >> > Thanks ! >> > >> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c >> > index 4468e1adc094..d5e68ee63b8f 100644 >> > --- a/net/ipv4/udp.c >> > +++ b/net/ipv4/udp.c >> > @@ -1004,8 +1004,11 @@ int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, >> > if ((rt->rt_flags & RTCF_BROADCAST) && >> > !sock_flag(sk, SOCK_BROADCAST)) >> > goto out; >> > - if (connected) >> > - sk_dst_set(sk, dst_clone(&rt->dst)); >> > + if (connected) { >> > + spin_lock_bh(&sk->sk_lock.slock); >> > + __sk_dst_set(sk, dst_clone(&rt->dst)); >> > + spin_unlock_bh(&sk->sk_lock.slock); >> > + } >> >> Nice catch. >> Should then we change sk_dst_set() itself to do spin_lock_bh unconditionally? >> Seems overhead is smaller, than checking all possible callsites manually. >> >> cc-ing Dormando as well. > > > Real problem is that sk_dst_set() uses a different lock. I never > understood how this was supposed to work. we probably need to test the assumption in the sk_dst_set() comment: /* This can be called while sk is owned by the caller only */ I don't understand why this piece of code doesn't do: old_dst = rcu_dereference_check(sk->sk_dst_cache, sock_owned_by_user(sk) || lockdep_is_held(&sk->sk_lock.slock)); like sk_dst_get does... If I'm reading the code correctly, at the time of sk_dst_set() call from udp_sendmsg() the sk_lock.slock is not held and sock_owned_by_user(sk) is false as well. Same not held condition is in the first sk_dst_reset() call from ip4_datagram_connect(). Though the lock is properly held from release_sock()->ip4_datagram_release_cb() Cannot agree more with Eric "how is it supposed to work?" > We should either : > > 1) use xchg() and no lock at all to change sk_dst_cache, as we did for > sk_rx_dst ( cf udp_sk_rx_dst_set() ) > > 2) No longer use sk_dst_lock, and always use the socket lock > (sk->sk_lock.slock) instead. Probably needs some combination of both. sk_dst_lock seems useless for ipv4. What the following suppose to do in ipv6_update_options() ?! spin_lock(&sk->sk_dst_lock); opt = xchg(&inet6_sk(sk)->opt, opt); spin_unlock(&sk->sk_dst_lock); seems ipv6 is reusing the same lock for completely different reason. > > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, 2014-06-06 at 10:44 -0700, Alexei Starovoitov wrote: > On Fri, Jun 6, 2014 at 9:16 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > > We should either : > > > > 1) use xchg() and no lock at all to change sk_dst_cache, as we did for > > sk_rx_dst ( cf udp_sk_rx_dst_set() ) > > > > 2) No longer use sk_dst_lock, and always use the socket lock > > (sk->sk_lock.slock) instead. > > Probably needs some combination of both. I do not think so. If we use xchg(), then we do not need anything else. If we use a spinlock, then xchg() seems useless. Any combination is buggy. In the past, UDP transmit was holding socket lock, but we added a lockless path, and I suppose more people use a UDP socket from different threads. Then, Steffen added the ip4_datagram_release_cb() thing, increasing the chance of mixing both 'protections'. Setting sk_dst_cache should hardly be a hot path. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Jun 6, 2014 at 10:56 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > On Fri, 2014-06-06 at 10:44 -0700, Alexei Starovoitov wrote: >> On Fri, Jun 6, 2014 at 9:16 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > >> > We should either : >> > >> > 1) use xchg() and no lock at all to change sk_dst_cache, as we did for >> > sk_rx_dst ( cf udp_sk_rx_dst_set() ) >> > >> > 2) No longer use sk_dst_lock, and always use the socket lock >> > (sk->sk_lock.slock) instead. >> >> Probably needs some combination of both. > > I do not think so. > > If we use xchg(), then we do not need anything else. > > If we use a spinlock, then xchg() seems useless. > > Any combination is buggy. > > In the past, UDP transmit was holding socket lock, > but we added a lockless path, and I suppose more people > use a UDP socket from different threads. > > Then, Steffen added the ip4_datagram_release_cb() thing, > increasing the chance of mixing both 'protections'. > > Setting sk_dst_cache should hardly be a hot path. yeah. if we use sk_lock.slock then xchg is obviously not needed. By 'both' I meant to do xchg() and get rid of sk_dst_lock to speed it up. Though not worth going too fancy if speed is not needed. > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 4468e1adc094..d5e68ee63b8f 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1004,8 +1004,11 @@ int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, if ((rt->rt_flags & RTCF_BROADCAST) && !sock_flag(sk, SOCK_BROADCAST)) goto out; - if (connected) - sk_dst_set(sk, dst_clone(&rt->dst)); + if (connected) { + spin_lock_bh(&sk->sk_lock.slock); + __sk_dst_set(sk, dst_clone(&rt->dst)); + spin_unlock_bh(&sk->sk_lock.slock); + } } if (msg->msg_flags&MSG_CONFIRM)