| Message ID | 20210308192113.2721435-1-weiwan@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | [net] ipv6: fix suspecious RCU usage warning | expand |
[ cc Ido and Petr ] On 3/8/21 12:21 PM, Wei Wang wrote: > diff --git a/include/net/nexthop.h b/include/net/nexthop.h > index 7bc057aee40b..48956b144689 100644 > --- a/include/net/nexthop.h > +++ b/include/net/nexthop.h > @@ -410,31 +410,39 @@ static inline struct fib_nh *fib_info_nh(struct fib_info *fi, int nhsel) > int fib6_check_nexthop(struct nexthop *nh, struct fib6_config *cfg, > struct netlink_ext_ack *extack); > > -static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh) > +static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh, > + bool bh_disabled) Hi Wei: I would prefer not to have a second argument to nexthop_fib6_nh for 1 code path, and a control path at that. > { > struct nh_info *nhi; > > if (nh->is_group) { > struct nh_group *nh_grp; > > - nh_grp = rcu_dereference_rtnl(nh->nh_grp); > + if (bh_disabled) > + nh_grp = rcu_dereference_bh_rtnl(nh->nh_grp); > + else > + nh_grp = rcu_dereference_rtnl(nh->nh_grp); > nh = nexthop_mpath_select(nh_grp, 0); > if (!nh) > return NULL; > } > > - nhi = rcu_dereference_rtnl(nh->nh_info); > + if (bh_disabled) > + nhi = rcu_dereference_bh_rtnl(nh->nh_info); > + else > + nhi = rcu_dereference_rtnl(nh->nh_info); > if (nhi->family == AF_INET6) > return &nhi->fib6_nh; > > return NULL; > } > I am wary of duplicating code, but this helper is simple enough that it should be ok with proper documentation. Ido/Petr: I think your resilient hashing patch set touches this helper. How ugly does it get to have a second version?
On Mon, Mar 08, 2021 at 07:47:31PM -0700, David Ahern wrote: > [ cc Ido and Petr ] > > On 3/8/21 12:21 PM, Wei Wang wrote: > > diff --git a/include/net/nexthop.h b/include/net/nexthop.h > > index 7bc057aee40b..48956b144689 100644 > > --- a/include/net/nexthop.h > > +++ b/include/net/nexthop.h > > @@ -410,31 +410,39 @@ static inline struct fib_nh *fib_info_nh(struct fib_info *fi, int nhsel) > > int fib6_check_nexthop(struct nexthop *nh, struct fib6_config *cfg, > > struct netlink_ext_ack *extack); > > > > -static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh) > > +static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh, > > + bool bh_disabled) > > Hi Wei: I would prefer not to have a second argument to nexthop_fib6_nh > for 1 code path, and a control path at that. > > > { > > struct nh_info *nhi; > > > > if (nh->is_group) { > > struct nh_group *nh_grp; > > > > - nh_grp = rcu_dereference_rtnl(nh->nh_grp); > > + if (bh_disabled) > > + nh_grp = rcu_dereference_bh_rtnl(nh->nh_grp); > > + else > > + nh_grp = rcu_dereference_rtnl(nh->nh_grp); > > nh = nexthop_mpath_select(nh_grp, 0); > > if (!nh) > > return NULL; > > } > > > > - nhi = rcu_dereference_rtnl(nh->nh_info); > > + if (bh_disabled) > > + nhi = rcu_dereference_bh_rtnl(nh->nh_info); > > + else > > + nhi = rcu_dereference_rtnl(nh->nh_info); > > if (nhi->family == AF_INET6) > > return &nhi->fib6_nh; > > > > return NULL; > > } > > > > I am wary of duplicating code, but this helper is simple enough that it > should be ok with proper documentation. > > Ido/Petr: I think your resilient hashing patch set touches this helper. > How ugly does it get to have a second version? It actually doesn't touch this helper. Looks fine to me: diff --git a/include/net/nexthop.h b/include/net/nexthop.h index ba94868a21d5..6df9c12546fd 100644 --- a/include/net/nexthop.h +++ b/include/net/nexthop.h @@ -496,6 +496,26 @@ static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh) return NULL; } +static inline struct fib6_nh *nexthop_fib6_nh_bh(struct nexthop *nh) +{ + struct nh_info *nhi; + + if (nh->is_group) { + struct nh_group *nh_grp; + + nh_grp = rcu_dereference_bh(nh->nh_grp); + nh = nexthop_mpath_select(nh_grp, 0); + if (!nh) + return NULL; + } + + nhi = rcu_dereference_bh(nh->nh_info); + if (nhi->family == AF_INET6) + return &nhi->fib6_nh; + + return NULL; +} + static inline struct net_device *fib6_info_nh_dev(struct fib6_info *f6i) { struct fib6_nh *fib6_nh; diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index ef9d022e693f..679699e953f1 100644 --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -2486,7 +2486,7 @@ static int ipv6_route_native_seq_show(struct seq_file *seq, void *v) const struct net_device *dev; if (rt->nh) - fib6_nh = nexthop_fib6_nh(rt->nh); + fib6_nh = nexthop_fib6_nh_bh(rt->nh); seq_printf(seq, "%pi6 %02x ", &rt->fib6_dst.addr, rt->fib6_dst.plen);
On Tue, Mar 9, 2021 at 11:33 AM David Ahern <dsahern@gmail.com> wrote: > > On 3/9/21 10:32 AM, Wei Wang wrote: > > Thanks David and Ido. > > To clarify, David, you suggest we add a separate function instead of > > adding an extra parameter, right? > > for this case I think it is the better way to go. OK. Will send out v2 for this.
diff --git a/include/net/nexthop.h b/include/net/nexthop.h index 7bc057aee40b..48956b144689 100644 --- a/include/net/nexthop.h +++ b/include/net/nexthop.h @@ -410,31 +410,39 @@ static inline struct fib_nh *fib_info_nh(struct fib_info *fi, int nhsel) int fib6_check_nexthop(struct nexthop *nh, struct fib6_config *cfg, struct netlink_ext_ack *extack); -static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh) +static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh, + bool bh_disabled) { struct nh_info *nhi; if (nh->is_group) { struct nh_group *nh_grp; - nh_grp = rcu_dereference_rtnl(nh->nh_grp); + if (bh_disabled) + nh_grp = rcu_dereference_bh_rtnl(nh->nh_grp); + else + nh_grp = rcu_dereference_rtnl(nh->nh_grp); nh = nexthop_mpath_select(nh_grp, 0); if (!nh) return NULL; } - nhi = rcu_dereference_rtnl(nh->nh_info); + if (bh_disabled) + nhi = rcu_dereference_bh_rtnl(nh->nh_info); + else + nhi = rcu_dereference_rtnl(nh->nh_info); if (nhi->family == AF_INET6) return &nhi->fib6_nh; return NULL; } +// Called with rcu_read_lock() static inline struct net_device *fib6_info_nh_dev(struct fib6_info *f6i) { struct fib6_nh *fib6_nh; - fib6_nh = f6i->nh ? nexthop_fib6_nh(f6i->nh) : f6i->fib6_nh; + fib6_nh = f6i->nh ? nexthop_fib6_nh(f6i->nh, false) : f6i->fib6_nh; return fib6_nh->fib_nh_dev; } @@ -449,7 +457,7 @@ static inline void nexthop_path_fib6_result(struct fib6_result *res, int hash) if (nhi->reject_nh) { res->fib6_type = RTN_BLACKHOLE; res->fib6_flags |= RTF_REJECT; - res->nh = nexthop_fib6_nh(nh); + res->nh = nexthop_fib6_nh(nh, false); } else { res->nh = &nhi->fib6_nh; } diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index ef9d022e693f..70246a7e1344 100644 --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -2486,7 +2486,7 @@ static int ipv6_route_native_seq_show(struct seq_file *seq, void *v) const struct net_device *dev; if (rt->nh) - fib6_nh = nexthop_fib6_nh(rt->nh); + fib6_nh = nexthop_fib6_nh(rt->nh, true); seq_printf(seq, "%pi6 %02x ", &rt->fib6_dst.addr, rt->fib6_dst.plen); diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 1536f4948e86..2439f6904806 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -547,7 +547,7 @@ static void rt6_device_match(struct net *net, struct fib6_result *res, if (!oif && ipv6_addr_any(saddr)) { if (unlikely(f6i->nh)) { - nh = nexthop_fib6_nh(f6i->nh); + nh = nexthop_fib6_nh(f6i->nh, false); if (nexthop_is_blackhole(f6i->nh)) goto out_blackhole; } else { @@ -583,7 +583,7 @@ static void rt6_device_match(struct net *net, struct fib6_result *res, } if (unlikely(f6i->nh)) { - nh = nexthop_fib6_nh(f6i->nh); + nh = nexthop_fib6_nh(f6i->nh, false); if (nexthop_is_blackhole(f6i->nh)) goto out_blackhole; } else { @@ -830,7 +830,7 @@ static void __find_rr_leaf(struct fib6_info *f6i_start, res->fib6_flags = RTF_REJECT; res->fib6_type = RTN_BLACKHOLE; res->f6i = f6i; - res->nh = nexthop_fib6_nh(f6i->nh); + res->nh = nexthop_fib6_nh(f6i->nh, false); return; } if (nexthop_for_each_fib6_nh(f6i->nh, rt6_nh_find_match, @@ -3701,7 +3701,7 @@ static struct fib6_info *ip6_route_info_create(struct fib6_config *cfg, goto out; } rt->nh = nh; - fib6_nh = nexthop_fib6_nh(rt->nh); + fib6_nh = nexthop_fib6_nh(rt->nh, false); } else { err = fib6_nh_init(net, rt->fib6_nh, cfg, gfp_flags, extack); if (err) @@ -5443,7 +5443,7 @@ static int rt6_fill_node_nexthop(struct sk_buff *skb, struct nexthop *nh, } else { struct fib6_nh *fib6_nh; - fib6_nh = nexthop_fib6_nh(nh); + fib6_nh = nexthop_fib6_nh(nh, false); if (fib_nexthop_info(skb, &fib6_nh->nh_common, AF_INET6, flags, false) < 0) goto nla_put_failure;
Syzbot reported the suspecious RCU usage in nexthop_fib6_nh() when called from ipv6_route_seq_show(). The reason is ipv6_route_seq_start() calls rcu_read_lock_bh(), while nexthop_fib6_nh() calls rcu_dereference_rtnl(). The fix proposed is to add an extra parameter in nexthop_fib6_nh() to indicate if bh is disabled or not, and then use the corresponding dereference function. The reported trace is as follows: ./include/net/nexthop.h:416 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 2 locks held by syz-executor.0/17895: #0: ffff8801db098e20 (&p->lock){+.+.}, at: seq_read+0x71/0x12a0 fs/seq_file.c:169 #1: ffffffff85e18de0 (rcu_read_lock_bh){....}, at: seq_file_net include/linux/seq_file_net.h:19 [inline] #1: ffffffff85e18de0 (rcu_read_lock_bh){....}, at: ipv6_route_seq_start+0xaf/0x300 net/ipv6/ip6_fib.c:2616 stack backtrace: CPU: 1 PID: 17895 Comm: syz-executor.0 Not tainted 4.15.0-syzkaller #0 Call Trace: [<ffffffff849edf9e>] __dump_stack lib/dump_stack.c:17 [inline] [<ffffffff849edf9e>] dump_stack+0xd8/0x147 lib/dump_stack.c:53 [<ffffffff8480b7fa>] lockdep_rcu_suspicious+0x153/0x15d kernel/locking/lockdep.c:5745 [<ffffffff8459ada6>] nexthop_fib6_nh include/net/nexthop.h:416 [inline] [<ffffffff8459ada6>] ipv6_route_native_seq_show net/ipv6/ip6_fib.c:2488 [inline] [<ffffffff8459ada6>] ipv6_route_seq_show+0x436/0x7a0 net/ipv6/ip6_fib.c:2673 [<ffffffff81c556df>] seq_read+0xccf/0x12a0 fs/seq_file.c:276 [<ffffffff81dbc62c>] proc_reg_read+0x10c/0x1d0 fs/proc/inode.c:231 [<ffffffff81bc28ae>] do_loop_readv_writev fs/read_write.c:714 [inline] [<ffffffff81bc28ae>] do_loop_readv_writev fs/read_write.c:701 [inline] [<ffffffff81bc28ae>] do_iter_read+0x49e/0x660 fs/read_write.c:935 [<ffffffff81bc81ab>] vfs_readv+0xfb/0x170 fs/read_write.c:997 [<ffffffff81c88847>] kernel_readv fs/splice.c:361 [inline] [<ffffffff81c88847>] default_file_splice_read+0x487/0x9c0 fs/splice.c:416 [<ffffffff81c86189>] do_splice_to+0x129/0x190 fs/splice.c:879 [<ffffffff81c86f66>] splice_direct_to_actor+0x256/0x890 fs/splice.c:951 [<ffffffff81c8777d>] do_splice_direct+0x1dd/0x2b0 fs/splice.c:1060 [<ffffffff81bc4747>] do_sendfile+0x597/0xce0 fs/read_write.c:1459 [<ffffffff81bca205>] SYSC_sendfile64 fs/read_write.c:1520 [inline] [<ffffffff81bca205>] SyS_sendfile64+0x155/0x170 fs/read_write.c:1506 [<ffffffff81015fcf>] do_syscall_64+0x1ff/0x310 arch/x86/entry/common.c:305 [<ffffffff84a00076>] entry_SYSCALL_64_after_hwframe+0x42/0xb7 Fixes: f88d8ea67fbdb ("ipv6: Plumb support for nexthop object in a fib6_info") Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: Wei Wang <weiwan@google.com> Cc: David Ahern <dsahern@kernel.org> Cc: Eric Dumazet <edumazet@google.com> --- include/net/nexthop.h | 18 +++++++++++++----- net/ipv6/ip6_fib.c | 2 +- net/ipv6/route.c | 10 +++++----- 3 files changed, 19 insertions(+), 11 deletions(-)