| Message ID | 1539840004-26433-2-git-send-email-john.fastabend@gmail.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | Fix kcm + sockmap by checking psock type | expand |
On 10/17/2018 10:20 PM, John Fastabend wrote: > Before using the psock returned by sk_psock_get() when adding it to a > sockmap we need to ensure it is actually a sockmap based psock. > Previously we were only checking this after incrementing the reference > counter which was an error. This resulted in a slab-out-of-bounds > error when the psock was not actually a sockmap type. > > This moves the check up so the reference counter is only used > if it is a sockmap psock. > > Eric reported the following KASAN BUG, > > BUG: KASAN: slab-out-of-bounds in atomic_read include/asm-generic/atomic-instrumented.h:21 [inline] > BUG: KASAN: slab-out-of-bounds in refcount_inc_not_zero_checked+0x97/0x2f0 lib/refcount.c:120 > Read of size 4 at addr ffff88019548be58 by task syz-executor4/22387 > > CPU: 1 PID: 22387 Comm: syz-executor4 Not tainted 4.19.0-rc7+ #264 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113 > print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256 > kasan_report_error mm/kasan/report.c:354 [inline] > kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412 > check_memory_region_inline mm/kasan/kasan.c:260 [inline] > check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267 > kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272 > atomic_read include/asm-generic/atomic-instrumented.h:21 [inline] > refcount_inc_not_zero_checked+0x97/0x2f0 lib/refcount.c:120 > sk_psock_get include/linux/skmsg.h:379 [inline] > sock_map_link.isra.6+0x41f/0xe30 net/core/sock_map.c:178 > sock_hash_update_common+0x19b/0x11e0 net/core/sock_map.c:669 > sock_hash_update_elem+0x306/0x470 net/core/sock_map.c:738 > map_update_elem+0x819/0xdf0 kernel/bpf/syscall.c:818 > > Signed-off-by: John Fastabend <john.fastabend@gmail.com> > Reported-by: Eric Dumazet <eric.dumazet@gmail.com> > Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface") > --- > include/linux/skmsg.h | 25 ++++++++++++++++++++----- > net/core/sock_map.c | 11 ++++++----- > 2 files changed, 26 insertions(+), 10 deletions(-) > > diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h > index 677b673..f44ca6b 100644 > --- a/include/linux/skmsg.h > +++ b/include/linux/skmsg.h > @@ -275,11 +275,6 @@ static inline struct sk_psock *sk_psock(const struct sock *sk) > return rcu_dereference_sk_user_data(sk); > } > > -static inline bool sk_has_psock(struct sock *sk) > -{ > - return sk_psock(sk) != NULL && sk->sk_prot->recvmsg == tcp_bpf_recvmsg; > -} > - > static inline void sk_psock_queue_msg(struct sk_psock *psock, > struct sk_msg *msg) > { > @@ -379,6 +374,26 @@ static inline bool sk_psock_test_state(const struct sk_psock *psock, > return test_bit(bit, &psock->state); > } > > +static inline struct sk_psock *sk_psock_get_checked(struct sock *sk) > +{ > + struct sk_psock *psock; > + > + rcu_read_lock(); > + psock = sk_psock(sk); > + if (psock) { > + if (sk->sk_prot->recvmsg != tcp_bpf_recvmsg) { > + psock = ERR_PTR(-EBUSY); > + goto out; > + } > + > + if (!refcount_inc_not_zero(&psock->refcnt)) > + psock = NULL; Caller is using IS_ERR(), so you probably want to : psock = ERR_PTR(-E<something>); > + } > +out: > + rcu_read_unlock(); > + return psock; > +} > + > static inline struct sk_psock *sk_psock_get(struct sock *sk) > { > struct sk_psock *psock; > diff --git a/net/core/sock_map.c b/net/core/sock_map.c > index 3c0e44c..be6092a 100644 > --- a/net/core/sock_map.c > +++ b/net/core/sock_map.c > @@ -175,12 +175,13 @@ static int sock_map_link(struct bpf_map *map, struct sk_psock_progs *progs, > } > } > > - psock = sk_psock_get(sk); > + psock = sk_psock_get_checked(sk); > + if (IS_ERR(psock)) { > + ret = PTR_ERR(psock); > + goto out_progs; > + } > + > if (psock) { > - if (!sk_has_psock(sk)) { > - ret = -EBUSY; > - goto out_progs; > - } > if ((msg_parser && READ_ONCE(psock->progs.msg_parser)) || > (skb_progs && READ_ONCE(psock->progs.skb_parser))) { > sk_psock_put(sk, psock); >
On 10/18/2018 10:34 AM, Eric Dumazet wrote: > > > On 10/17/2018 10:20 PM, John Fastabend wrote: >> Before using the psock returned by sk_psock_get() when adding it to a >> sockmap we need to ensure it is actually a sockmap based psock. >> Previously we were only checking this after incrementing the reference >> counter which was an error. This resulted in a slab-out-of-bounds >> error when the psock was not actually a sockmap type. >> >> This moves the check up so the reference counter is only used >> if it is a sockmap psock. >> >> Eric reported the following KASAN BUG, >> >> BUG: KASAN: slab-out-of-bounds in atomic_read include/asm-generic/atomic-instrumented.h:21 [inline] >> BUG: KASAN: slab-out-of-bounds in refcount_inc_not_zero_checked+0x97/0x2f0 lib/refcount.c:120 >> Read of size 4 at addr ffff88019548be58 by task syz-executor4/22387 >> >> CPU: 1 PID: 22387 Comm: syz-executor4 Not tainted 4.19.0-rc7+ #264 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 >> Call Trace: >> __dump_stack lib/dump_stack.c:77 [inline] >> dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113 >> print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256 >> kasan_report_error mm/kasan/report.c:354 [inline] >> kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412 >> check_memory_region_inline mm/kasan/kasan.c:260 [inline] >> check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267 >> kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272 >> atomic_read include/asm-generic/atomic-instrumented.h:21 [inline] >> refcount_inc_not_zero_checked+0x97/0x2f0 lib/refcount.c:120 >> sk_psock_get include/linux/skmsg.h:379 [inline] >> sock_map_link.isra.6+0x41f/0xe30 net/core/sock_map.c:178 >> sock_hash_update_common+0x19b/0x11e0 net/core/sock_map.c:669 >> sock_hash_update_elem+0x306/0x470 net/core/sock_map.c:738 >> map_update_elem+0x819/0xdf0 kernel/bpf/syscall.c:818 >> >> Signed-off-by: John Fastabend <john.fastabend@gmail.com> >> Reported-by: Eric Dumazet <eric.dumazet@gmail.com> >> Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface") >> --- [...] >> +static inline struct sk_psock *sk_psock_get_checked(struct sock *sk) >> +{ >> + struct sk_psock *psock; >> + >> + rcu_read_lock(); >> + psock = sk_psock(sk); >> + if (psock) { >> + if (sk->sk_prot->recvmsg != tcp_bpf_recvmsg) { >> + psock = ERR_PTR(-EBUSY); >> + goto out; >> + } >> + >> + if (!refcount_inc_not_zero(&psock->refcnt)) >> + psock = NULL; > > Caller is using IS_ERR(), so you probably want to : > > psock = ERR_PTR(-E<something>); > > Yeah we can make this EBUSY as well. Originally I was thinking that we could create the psock and attach it in this case but it would be racy and require an rcu sync most likely. To hit this case users would need to have multiple maps and be adding/deleting socks from those maps at the same time. Seems pretty rare and not worth punishing the normal case with synchronization. Nice catch. .John
diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h index 677b673..f44ca6b 100644 --- a/include/linux/skmsg.h +++ b/include/linux/skmsg.h @@ -275,11 +275,6 @@ static inline struct sk_psock *sk_psock(const struct sock *sk) return rcu_dereference_sk_user_data(sk); } -static inline bool sk_has_psock(struct sock *sk) -{ - return sk_psock(sk) != NULL && sk->sk_prot->recvmsg == tcp_bpf_recvmsg; -} - static inline void sk_psock_queue_msg(struct sk_psock *psock, struct sk_msg *msg) { @@ -379,6 +374,26 @@ static inline bool sk_psock_test_state(const struct sk_psock *psock, return test_bit(bit, &psock->state); } +static inline struct sk_psock *sk_psock_get_checked(struct sock *sk) +{ + struct sk_psock *psock; + + rcu_read_lock(); + psock = sk_psock(sk); + if (psock) { + if (sk->sk_prot->recvmsg != tcp_bpf_recvmsg) { + psock = ERR_PTR(-EBUSY); + goto out; + } + + if (!refcount_inc_not_zero(&psock->refcnt)) + psock = NULL; + } +out: + rcu_read_unlock(); + return psock; +} + static inline struct sk_psock *sk_psock_get(struct sock *sk) { struct sk_psock *psock; diff --git a/net/core/sock_map.c b/net/core/sock_map.c index 3c0e44c..be6092a 100644 --- a/net/core/sock_map.c +++ b/net/core/sock_map.c @@ -175,12 +175,13 @@ static int sock_map_link(struct bpf_map *map, struct sk_psock_progs *progs, } } - psock = sk_psock_get(sk); + psock = sk_psock_get_checked(sk); + if (IS_ERR(psock)) { + ret = PTR_ERR(psock); + goto out_progs; + } + if (psock) { - if (!sk_has_psock(sk)) { - ret = -EBUSY; - goto out_progs; - } if ((msg_parser && READ_ONCE(psock->progs.msg_parser)) || (skb_progs && READ_ONCE(psock->progs.skb_parser))) { sk_psock_put(sk, psock);
Before using the psock returned by sk_psock_get() when adding it to a sockmap we need to ensure it is actually a sockmap based psock. Previously we were only checking this after incrementing the reference counter which was an error. This resulted in a slab-out-of-bounds error when the psock was not actually a sockmap type. This moves the check up so the reference counter is only used if it is a sockmap psock. Eric reported the following KASAN BUG, BUG: KASAN: slab-out-of-bounds in atomic_read include/asm-generic/atomic-instrumented.h:21 [inline] BUG: KASAN: slab-out-of-bounds in refcount_inc_not_zero_checked+0x97/0x2f0 lib/refcount.c:120 Read of size 4 at addr ffff88019548be58 by task syz-executor4/22387 CPU: 1 PID: 22387 Comm: syz-executor4 Not tainted 4.19.0-rc7+ #264 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412 check_memory_region_inline mm/kasan/kasan.c:260 [inline] check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267 kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272 atomic_read include/asm-generic/atomic-instrumented.h:21 [inline] refcount_inc_not_zero_checked+0x97/0x2f0 lib/refcount.c:120 sk_psock_get include/linux/skmsg.h:379 [inline] sock_map_link.isra.6+0x41f/0xe30 net/core/sock_map.c:178 sock_hash_update_common+0x19b/0x11e0 net/core/sock_map.c:669 sock_hash_update_elem+0x306/0x470 net/core/sock_map.c:738 map_update_elem+0x819/0xdf0 kernel/bpf/syscall.c:818 Signed-off-by: John Fastabend <john.fastabend@gmail.com> Reported-by: Eric Dumazet <eric.dumazet@gmail.com> Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface") --- include/linux/skmsg.h | 25 ++++++++++++++++++++----- net/core/sock_map.c | 11 ++++++----- 2 files changed, 26 insertions(+), 10 deletions(-)