net: slice bounds out of range

[anacrolix]

What version of Go are you using (go version)?

$ go version
go version go1.21rc2 darwin/arm64

Does this issue reproduce with the latest release?

It occurs with 1.21, 1.20, and earlier version too (untested)

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
darwin/amd64

What did you do?

Probably try to resolve an IP

What did you expect to see?

It resolve

What did you see instead?

panic: runtime error: slice bounds out of range [54:45]

goroutine 65 [running]:
internal/poll.(*FD).Write(0xc0001f6080, {0xc00015e002, 0x2d, 0x200})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/internal/poll/fd_unix.go:383 +0x49c
net.(*netFD).Write(0xc0001f6080, {0xc00015e002, 0x2d, 0x200})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/fd_posix.go:96 +0x48
net.(*conn).Write(0xc0001200e0, {0xc00015e002, 0x2d, 0x200})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/net.go:195 +0x88
net.dnsPacketRoundTrip({_, _}, _, {{{0x6d, 0x79, 0x69, 0x70, 0x2e, 0x6f, 0x70, ...}, ...}, ...}, ...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:102 +0x88
net.(*Resolver).exchange(_, {_, _}, {_, _}, {{{0x6d, 0x79, 0x69, 0x70, 0x2e, ...}, ...}, ...}, ...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:187 +0x3ec
net.(*Resolver).tryOneName(_, {_, _}, _, {_, _}, _)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:277 +0x40c
net.(*Resolver).goLookupIPCNAMEOrder.func3.1(0x1c?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:653 +0xa0
created by net.(*Resolver).goLookupIPCNAMEOrder.func3
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:652 +0x244

[anacrolix]

I believe it has something to do with DNS over UDP over IPv6. I can reproduce it by running:

go install github.com/anacrolix/publicip/cmd/publicip
publicip -6

While using the Mullvad VPN. I suspect even if it's an edge case and the packet is being intercepted, it shouldn't be panicking my application.

[mengzhuo]

I believe it has something to do with DNS over UDP over IPv6. I can reproduce it by running:

go install github.com/anacrolix/publicip/cmd/publicip
publicip -6

While using the Mullvad VPN. I suspect even if it's an edge case and the packet is being intercepted, it shouldn't be panicking my application.

I can run this command without error on linux/amd64, platform related issue?

[bcmills]

panic: runtime error: slice bounds out of range [54:45]

goroutine 65 [running]:
internal/poll.(*FD).Write(0xc0001f6080, {0xc00015e002, 0x2d, 0x200})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/internal/poll/fd_unix.go:383 +0x49c

The relevant block of code (in go1.20.3) is here:
https://cs.opensource.google/go/go/+/refs/tags/go1.20.3:src/internal/poll/fd_unix.go;l=379-386;drc=a2baae6851a157d662dff7cc508659f66249698a

That would seem to imply that at that point nn is 54 and max is 45.

• The upper bound on max is len(p) or nn + maxRW, whichever is smaller. (maxRW is 1 << 30, so in this case it must be len(p).)
• The Write loop terminates when nn == len(p) after a call to syscall.Write with a slice of length max - nn.
• The loop terminates when nn == len(p), and increments nn by the number of bytes reported by syscall.Write.

Unfortunately, the most plausible explanations both seem unlikely:

• either the previous syscall.Write returned an n larger than len(p[nn:max]),
• or a something in the program (cgo, or unsafe, or a bug in runtime or syscall, or a kernel or libc bug?) corrupted some local variable in (*FD).Write or syscall.Write or syscall.write.

The latter possibility makes me think of #60449, but note that that is for amd64 whereas this report is for arm64.

But the fact that this reproduces for you “[w]hile using the Mullvad VPN” makes me wonder if something about the VPN is causing the libc write call to return an incorrect count. Perhaps (*FD).Write should check for that explicitly and return an error for it?

(CC @ianlancetaylor, @golang/runtime)

[bcmills]

Wait, no. In that stack trace goroutine 65 is running, not panicking. Maybe that goroutine stack is a red herring.

@anacrolix, can you post the complete goroutine dump from a failure?

[anacrolix]

Thank you for looking into this @bcmills. That's actually the only thing it outputs when it crashes. Here it is with

GOTRACEBACK=system

% GOTRACEBACK=system godo -v -- ./cmd/publicip -6
godo: starting publicip
panic: runtime error: slice bounds out of range [48:45]

goroutine 34 [running]:
panic({0x104359ca0, 0x14000106138})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/panic.go:987 +0x3c0 fp=0x14000151e30 sp=0x14000151d70 pc=0x10409a2f0
runtime.goPanicSliceB(0x30, 0x2d)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/panic.go:153 +0x7c fp=0x14000151e70 sp=0x14000151e30 pc=0x1040986cc
internal/poll.(*FD).Write(0x14000158000, {0x14000154002, 0x2d, 0x200})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/internal/poll/fd_unix.go:383 +0x3ac fp=0x14000151f20 sp=0x14000151e70 pc=0x104121cac
net.(*netFD).Write(0x14000158000, {0x14000154002?, 0x0?, 0x104375198?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/fd_posix.go:96 +0x28 fp=0x14000151f70 sp=0x14000151f20 pc=0x10414d0b8
net.(*conn).Write(0x1400010e038, {0x14000154002?, 0x14000151fe8?, 0x1041476a4?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/net.go:195 +0x34 fp=0x14000151fc0 sp=0x14000151f70 pc=0x104157a04
net.(*UDPConn).Write(0x0?, {0x14000154002?, 0x14000152048?, 0x104145d64?})
	<autogenerated>:1 +0x2c fp=0x14000151ff0 sp=0x14000151fc0 pc=0x10416286c
net.dnsPacketRoundTrip({_, _}, _, {{{0x6d, 0x79, 0x69, 0x70, 0x2e, 0x6f, 0x70, ...}, ...}, ...}, ...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:102 +0x74 fp=0x140001525a0 sp=0x14000151ff0 pc=0x1041476d4
net.(*Resolver).exchange(_, {_, _}, {_, _}, {{{0x6d, 0x79, 0x69, 0x70, 0x2e, ...}, ...}, ...}, ...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:187 +0x38c fp=0x14000152ef0 sp=0x140001525a0 pc=0x1041483ec
net.(*Resolver).tryOneName(_, {_, _}, _, {_, _}, _)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:277 +0x368 fp=0x14000153a20 sp=0x14000152ef0 pc=0x1041491e8
net.(*Resolver).goLookupIPCNAMEOrder.func3.1(0x1c?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:653 +0x68 fp=0x14000153fb0 sp=0x14000153a20 pc=0x10414ba68
net.(*Resolver).goLookupIPCNAMEOrder.func3.2()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:656 +0x30 fp=0x14000153fd0 sp=0x14000153fb0 pc=0x10414b9c0
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x14000153fd0 sp=0x14000153fd0 pc=0x1040cb5d4
created by net.(*Resolver).goLookupIPCNAMEOrder.func3
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:652 +0x180

goroutine 1 [select]:
runtime.gopark(0x140000c1d40?, 0x3?, 0x78?, 0x1b?, 0x140000c1cba?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:381 +0xe4 fp=0x140000c1b20 sp=0x140000c1b00 pc=0x10409d0d4
runtime.selectgo(0x140000c1d40, 0x140000c1cb4, 0x140000c1c98?, 0x0, 0x140000c1c88?, 0x1)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/select.go:327 +0x690 fp=0x140000c1c40 sp=0x140000c1b20 pc=0x1040ad3b0
github.com/anacrolix/publicip.race[...]({0x104375ed8, 0x140000a2e40}, {0x140000c1e28, 0x2, 0x0})
	/Users/anacrolix/ags/publicip/async.go:31 +0x27c fp=0x140000c1d80 sp=0x140000c1c40 pc=0x1042692bc
github.com/anacrolix/publicip.Get({0x104375ed8, 0x140000a2e40}, {0x104286e23, 0x3})
	/Users/anacrolix/ags/publicip/publicip.go:80 +0xa8 fp=0x140000c1e40 sp=0x140000c1d80 pc=0x1042682b8
github.com/anacrolix/publicip.Get6({0x104375ea0, 0x140000a2e10})
	/Users/anacrolix/ags/publicip/publicip.go:111 +0x6c fp=0x140000c1e80 sp=0x140000c1e40 pc=0x1042686dc
main.main()
	/Users/anacrolix/ags/publicip/cmd/publicip/main.go:24 +0x128 fp=0x140000c1f70 sp=0x140000c1e80 pc=0x104286698
runtime.main()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:250 +0x248 fp=0x140000c1fd0 sp=0x140000c1f70 pc=0x10409cca8
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x140000c1fd0 sp=0x140000c1fd0 pc=0x1040cb5d4

goroutine 2 [force gc (idle)]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:381 +0xe4 fp=0x14000044fa0 sp=0x14000044f80 pc=0x10409d0d4
runtime.goparkunlock(...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:387
runtime.forcegchelper()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:305 +0xb8 fp=0x14000044fd0 sp=0x14000044fa0 pc=0x10409cf18
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x14000044fd0 sp=0x14000044fd0 pc=0x1040cb5d4
created by runtime.init.6
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:293 +0x24

goroutine 17 [GC sweep wait]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:381 +0xe4 fp=0x14000040760 sp=0x14000040740 pc=0x10409d0d4
runtime.goparkunlock(...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:387
runtime.bgsweep(0x0?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/mgcsweep.go:278 +0xa4 fp=0x140000407b0 sp=0x14000040760 pc=0x10408a354
runtime.gcenable.func1()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/mgc.go:178 +0x28 fp=0x140000407d0 sp=0x140000407b0 pc=0x10407f108
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x140000407d0 sp=0x140000407d0 pc=0x1040cb5d4
created by runtime.gcenable
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/mgc.go:178 +0x74

goroutine 18 [GC scavenge wait]:
runtime.gopark(0x1400008c000?, 0x1042fb4d0?, 0x1?, 0x0?, 0x0?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:381 +0xe4 fp=0x14000040f50 sp=0x14000040f30 pc=0x10409d0d4
runtime.goparkunlock(...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:387
runtime.(*scavengerState).park(0x10450a7a0)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/mgcscavenge.go:400 +0x5c fp=0x14000040f80 sp=0x14000040f50 pc=0x1040881dc
runtime.bgscavenge(0x0?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/mgcscavenge.go:628 +0x44 fp=0x14000040fb0 sp=0x14000040f80 pc=0x104088754
runtime.gcenable.func2()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/mgc.go:179 +0x28 fp=0x14000040fd0 sp=0x14000040fb0 pc=0x10407f0a8
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x14000040fd0 sp=0x14000040fd0 pc=0x1040cb5d4
created by runtime.gcenable
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/mgc.go:179 +0xb8

goroutine 19 [finalizer wait]:
runtime.gopark(0x140000445a8?, 0x6000010407cff8?, 0x48?, 0x15?, 0x1?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:381 +0xe4 fp=0x14000044580 sp=0x14000044560 pc=0x10409d0d4
runtime.runfinq()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/mfinal.go:193 +0x10c fp=0x140000447d0 sp=0x14000044580 pc=0x10407e19c
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x140000447d0 sp=0x140000447d0 pc=0x1040cb5d4
created by runtime.createfing
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/mfinal.go:163 +0x84

goroutine 20 [select]:
runtime.gopark(0x14000098c60?, 0x2?, 0x60?, 0xc0?, 0x14000098ba4?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:381 +0xe4 fp=0x140000989f0 sp=0x140000989d0 pc=0x10409d0d4
runtime.selectgo(0x14000098c60, 0x14000098ba0, 0x14?, 0x0, 0x0?, 0x1)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/select.go:327 +0x690 fp=0x14000098b10 sp=0x140000989f0 pc=0x1040ad3b0
net.(*Resolver).lookupIPAddr(0x1044ffae0, {0x104375e30?, 0x14000094280}, {0x104286e23, 0x3}, {0x10428a2a1, 0x10})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/lookup.go:334 +0x40c fp=0x14000098d00 sp=0x14000098b10 pc=0x104155dcc
net.(*Resolver).internetAddrList(0x104375e30?, {0x104375e30?, 0x14000094280?}, {0x104286e23, 0x3}, {0x10428a2a1?, 0x0?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/ipsock.go:288 +0x4e8 fp=0x14000098e30 sp=0x14000098d00 pc=0x104153ef8
net.(*Resolver).LookupIP(0x0?, {0x104375e30, 0x14000094280}, {0x104286e23, 0x3}, {0x10428a2a1, 0x10})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/lookup.go:232 +0x17c fp=0x14000098ed0 sp=0x14000098e30 pc=0x10415571c
github.com/anacrolix/publicip.Get.func1({0x104375e30?, 0x14000094280?})
	/Users/anacrolix/ags/publicip/publicip.go:83 +0x50 fp=0x14000098f30 sp=0x14000098ed0 pc=0x104268540
github.com/anacrolix/publicip.race[...].func1()
	/Users/anacrolix/ags/publicip/async.go:18 +0x4c fp=0x14000098fd0 sp=0x14000098f30 pc=0x10426886c
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x14000098fd0 sp=0x14000098fd0 pc=0x1040cb5d4
created by github.com/anacrolix/publicip.race[...]
	/Users/anacrolix/ags/publicip/async.go:17 +0x114

goroutine 21 [select]:
runtime.gopark(0x140000c36b0?, 0x4?, 0xe8?, 0x33?, 0x140000c3558?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:381 +0xe4 fp=0x140000c33c0 sp=0x140000c33a0 pc=0x10409d0d4
runtime.selectgo(0x140000c36b0, 0x140000c3550, 0x1400008ef80?, 0x0, 0x140000c3538?, 0x1)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/select.go:327 +0x690 fp=0x140000c34e0 sp=0x140000c33c0 pc=0x1040ad3b0
net/http.(*Transport).getConn(0x104504ae0, 0x140000b2200, {{}, 0x0, {0x140000ba120, 0x5}, {0x140000ba138, 0x11}, 0x0})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/transport.go:1382 +0x458 fp=0x140000c3700 sp=0x140000c34e0 pc=0x104256798
net/http.(*Transport).roundTrip(0x104504ae0, 0x140000fc200)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/transport.go:590 +0x690 fp=0x140000c3930 sp=0x140000c3700 pc=0x104252cb0
net/http.(*Transport).RoundTrip(0x1400009c978?, 0x104373f08?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/roundtrip.go:17 +0x1c fp=0x140000c3950 sp=0x140000c3930 pc=0x10424a53c
net/http.send(0x140000fc200, {0x104373f08, 0x104504ae0}, {0x10422b550?, 0x8?, 0x0?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/client.go:252 +0x520 fp=0x140000c3b50 sp=0x140000c3950 pc=0x104229f10
net/http.(*Client).send(0x1044ffea0, 0x140000fc200, {0x1400009cc18?, 0x104073778?, 0x0?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/client.go:176 +0x98 fp=0x140000c3bd0 sp=0x140000c3b50 pc=0x104229888
net/http.(*Client).do(0x1044ffea0, 0x140000fc200)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/client.go:716 +0x6f4 fp=0x140000c3de0 sp=0x140000c3bd0 pc=0x10422b5a4
net/http.(*Client).Do(...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/client.go:582
github.com/anacrolix/publicip.fromHttp({0x104375e30, 0x14000094280}, {0x0?, 0x0?})
	/Users/anacrolix/ags/publicip/http.go:30 +0xb0 fp=0x140000c3ed0 sp=0x140000c3de0 pc=0x104267bd0
github.com/anacrolix/publicip.Get.func2({0x104375e30?, 0x14000094280?})
	/Users/anacrolix/ags/publicip/publicip.go:86 +0x2c fp=0x140000c3f30 sp=0x140000c3ed0 pc=0x10426877c
github.com/anacrolix/publicip.race[...].func1()
	/Users/anacrolix/ags/publicip/async.go:18 +0x4c fp=0x140000c3fd0 sp=0x140000c3f30 pc=0x10426886c
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x140000c3fd0 sp=0x140000c3fd0 pc=0x1040cb5d4
created by github.com/anacrolix/publicip.race[...]
	/Users/anacrolix/ags/publicip/async.go:17 +0x114

goroutine 33 [chan receive]:
runtime.gopark(0x140000bc9f8?, 0x10407d044?, 0xf8?, 0xc9?, 0x1800010407cff8?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:381 +0xe4 fp=0x140000bc9c0 sp=0x140000bc9a0 pc=0x10409d0d4
runtime.chanrecv(0x1400010a240, 0x140000bcaa0, 0x1)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/chan.go:583 +0x45c fp=0x140000bca50 sp=0x140000bc9c0 pc=0x10406d76c
runtime.chanrecv1(0x140000bcaa8?, 0x104087700?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/chan.go:442 +0x14 fp=0x140000bca80 sp=0x140000bca50 pc=0x10406d2d4
net.(*Resolver).goLookupIPCNAMEOrder.func4({_, _}, _)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:659 +0x64 fp=0x140000bcc10 sp=0x140000bca80 pc=0x10414b7a4
net.(*Resolver).goLookupIPCNAMEOrder(_, {_, _}, {_, _}, {_, _}, _, _)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:669 +0x9ac fp=0x140000bd970 sp=0x140000bcc10 pc=0x10414addc
net.(*Resolver).goLookupIP(0x1044ffae0?, {0x104375e30, 0x14000104000}, {0x104286e23, 0x3}, {0x10428a2a1, 0x10})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dnsclient_unix.go:591 +0xb8 fp=0x140000bdbd0 sp=0x140000bd970 pc=0x10414a3b8
net.(*Resolver).lookupIP(0x104375e30?, {0x104375e30?, 0x14000104000?}, {0x104286e23?, 0x3?}, {0x10428a2a1?, 0x0?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/lookup_unix.go:70 +0x40 fp=0x140000bde30 sp=0x140000bdbd0 pc=0x104156f20
net.(*Resolver).lookupIP-fm({0x104375e30?, 0x14000104000?}, {0x104286e23?, 0x0?}, {0x10428a2a1?, 0x0?})
	<autogenerated>:1 +0x54 fp=0x140000bde80 sp=0x140000bde30 pc=0x1041635c4
net.glob..func1({0x104375e30?, 0x14000104000?}, 0x0?, {0x104286e23?, 0x14000094280?}, {0x10428a2a1?, 0x3?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/hook.go:23 +0x44 fp=0x140000bdec0 sp=0x140000bde80 pc=0x10414de14
net.(*Resolver).lookupIPAddr.func1()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/lookup.go:326 +0x48 fp=0x140000bdf20 sp=0x140000bdec0 pc=0x1041565b8
internal/singleflight.(*Group).doCall(0x1044ffaf0, 0x14000104050, {0x14000106000, 0x14}, 0x0?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/internal/singleflight/singleflight.go:93 +0x34 fp=0x140000bdf90 sp=0x140000bdf20 pc=0x10413fc64
internal/singleflight.(*Group).DoChan.func1()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/internal/singleflight/singleflight.go:86 +0x38 fp=0x140000bdfd0 sp=0x140000bdf90 pc=0x10413fbf8
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x140000bdfd0 sp=0x140000bdfd0 pc=0x1040cb5d4
created by internal/singleflight.(*Group).DoChan
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/internal/singleflight/singleflight.go:86 +0x3b4

goroutine 22 [IO wait]:
runtime.gopark(0x140000b22c0?, 0x40?, 0x38?, 0x0?, 0x104359680?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:381 +0xe4 fp=0x14000184d80 sp=0x14000184d60 pc=0x10409d0d4
runtime.netpollblock(0x14000184dd8?, 0x40a5d18?, 0x1?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/netpoll.go:527 +0x158 fp=0x14000184dc0 sp=0x14000184d80 pc=0x104096828
internal/poll.runtime_pollWait(0x12ba76628, 0x77)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/netpoll.go:306 +0xa0 fp=0x14000184df0 sp=0x14000184dc0 pc=0x1040c5b60
internal/poll.(*pollDesc).wait(0x140000f0300?, 0x0?, 0x0)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/internal/poll/fd_poll_runtime.go:84 +0x28 fp=0x14000184e20 sp=0x14000184df0 pc=0x104120e88
internal/poll.(*pollDesc).waitWrite(...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/internal/poll/fd_poll_runtime.go:93
internal/poll.(*FD).WaitWrite(...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/internal/poll/fd_unix.go:741
net.(*netFD).connect(0x140000f0300, {0x104375ea0?, 0x140000a3170}, {0x0?, 0x14000185058?}, {0x104374208?, 0x140000b81c0?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/fd_unix.go:141 +0x5a0 fp=0x14000184fc0 sp=0x14000184e20 pc=0x10414d7e0
net.(*netFD).dial(0x140000f0300, {0x104375ea0, 0x140000a3170}, {0x1043767f8?, 0x0?}, {0x1043767f8?, 0x140000a3110}, 0x104073c24?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/sock_posix.go:151 +0x324 fp=0x14000185090 sp=0x14000184fc0 pc=0x10415bd24
net.socket({0x104375ea0, 0x140000a3170}, {0x140000a6278, 0x4}, 0x1e, 0x1, 0x104286f9a?, 0xa0?, {0x1043767f8?, 0x0}, ...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/sock_posix.go:70 +0x220 fp=0x14000185150 sp=0x14000185090 pc=0x10415b900
net.internetSocket({0x104375ea0, 0x140000a3170}, {0x140000a6278, 0x4}, {0x1043767f8, 0x0}, {0x1043767f8, 0x140000a3110}, 0x14000185258?, 0x104073778?, ...)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/ipsock_posix.go:142 +0xa8 fp=0x140001851e0 sp=0x14000185150 pc=0x104154b78
net.(*sysDialer).doDialTCP(0x140000fe1b0, {0x104375ea0, 0x140000a3170}, 0x0, 0x140001852f8?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/tcpsock_posix.go:74 +0xac fp=0x140001852a0 sp=0x140001851e0 pc=0x10415e0ac
net.(*sysDialer).dialTCP(0x27dfd8da34c01?, {0x104375ea0?, 0x140000a3170?}, 0x104098cb4?, 0x104375e30?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/tcpsock_posix.go:64 +0x70 fp=0x140001852e0 sp=0x140001852a0 pc=0x10415df80
net.(*sysDialer).dialSingle(0x140000fe1b0, {0x104375ea0, 0x140000a3170}, {0x104375170?, 0x140000a3110})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dial.go:580 +0x188 fp=0x140001853b0 sp=0x140001852e0 pc=0x104146a68
net.(*sysDialer).dialSerial(0x140000fe1b0, {0x104375e30, 0x14000094280}, {0x14000090280?, 0x2, 0x14000094370?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dial.go:548 +0x190 fp=0x140001854c0 sp=0x140001853b0 pc=0x104146490
net.(*sysDialer).dialParallel(0xc11fc724476a02a0?, {0x104375e30?, 0x14000094280?}, {0x14000090280?, 0x4?, 0x140000a6278?}, {0x0?, 0x140000ba138?, 0x11?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dial.go:449 +0x2f0 fp=0x14000185720 sp=0x140001854c0 pc=0x104145d50
net.(*Dialer).DialContext(0x140001858a0, {0x104375e30, 0x14000094280}, {0x140000a6278, 0x4}, {0x140000ba138, 0x11})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/dial.go:440 +0x5ac fp=0x14000185860 sp=0x14000185720 pc=0x1041458ec
github.com/anacrolix/publicip.dialContext({0x104375e30, 0x14000094280}, {0x104286e44, 0x3}, {0x140000ba138, 0x11})
	/Users/anacrolix/ags/publicip/publicip.go:25 +0xe0 fp=0x14000185910 sp=0x14000185860 pc=0x104268040
net/http.(*Transport).dial(0x140000a2f30?, {0x104375e30?, 0x14000094280?}, {0x104286e44?, 0x1400009ca08?}, {0x140000ba138?, 0x1400009c9c8?})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/transport.go:1176 +0xdc fp=0x14000185970 sp=0x14000185910 pc=0x104255bdc
net/http.(*Transport).dialConn(0x104504ae0, {0x104375e30, 0x14000094280}, {{}, 0x0, {0x140000ba120, 0x5}, {0x140000ba138, 0x11}, 0x0})
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/transport.go:1614 +0x654 fp=0x14000185ec0 sp=0x14000185970 pc=0x104258414
net/http.(*Transport).dialConnFor(0x0?, 0x140000d62c0)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/transport.go:1456 +0x7c fp=0x14000185fb0 sp=0x14000185ec0 pc=0x1042571dc
net/http.(*Transport).queueForDial.func1()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/transport.go:1425 +0x2c fp=0x14000185fd0 sp=0x14000185fb0 pc=0x10425712c
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x14000185fd0 sp=0x14000185fd0 pc=0x1040cb5d4
created by net/http.(*Transport).queueForDial
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/http/transport.go:1425 +0x398

goroutine 25 [select]:
runtime.gopark(0x140000427a8?, 0x2?, 0x0?, 0x0?, 0x1400004277c?)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/proc.go:381 +0xe4 fp=0x14000042610 sp=0x140000425f0 pc=0x10409d0d4
runtime.selectgo(0x140000427a8, 0x14000042778, 0x0?, 0x0, 0x0?, 0x1)
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/select.go:327 +0x690 fp=0x14000042730 sp=0x14000042610 pc=0x1040ad3b0
net.(*netFD).connect.func2()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/fd_unix.go:118 +0x70 fp=0x140000427d0 sp=0x14000042730 pc=0x10414db80
runtime.goexit()
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/runtime/asm_arm64.s:1172 +0x4 fp=0x140000427d0 sp=0x140000427d0 pc=0x1040cb5d4
created by net.(*netFD).connect
	/opt/homebrew/Cellar/go/1.20.3/libexec/src/net/fd_unix.go:117 +0x2f0

[n-canter]

We actually have a similar issue on Intel Macs (go1.20.3, go1.20.5): panics while connecting to VPN using Cisco AnyConnect.
arm64 macs running same go code compiled for Apple Silicon don't panic.

It seems, at some point syscall.Write returns 33554436.

panic: runtime error: slice bounds out of range [33554436:43]
goroutine 7738 [running]:
internal/poll.(*FD).Write(0xc000842100, {0xc0005f01e0, 0x2b, 0x1c5})
  /usr/local/go/src/internal/poll/fd_unix.go:383 +0x4aa
net.(*netFD).Write(0xc000842100, {0xc0005f01e0?, 0xc000837890?, 0x100ed61e0?})
  /usr/local/go/src/net/fd_posix.go:96 +0x29
net.(*conn).Write(0xc000506000, {0xc0005f01e0?, 0xc0008378f0?, 0xc0005f01e0?})
  /usr/local/go/src/net/net.go:195 +0x45
crypto/tls.(*Conn).write(0xc0007dd500, {0xc0005f01e0?, 0x5?, 0x1c5?})
  /usr/local/go/src/crypto/tls/conn.go:923 +0x10d
crypto/tls.(*Conn).writeRecordLocked(0xc0007dd500, 0x17, {0xc000516000, 0x15, 0x1000})
  /usr/local/go/src/crypto/tls/conn.go:991 +0x354
crypto/tls.(*Conn).Write(0x0?, {0xc000516000, 0x15, 0x1000})
  /usr/local/go/src/crypto/tls/conn.go:1186 +0x411
net/http.http2stickyErrWriter.Write({{0x101381f18?, 0xc0007dd500?}, 0xc0004a2460?, 0xc0006602c0?}, {0xc000516000, 0x15, 0x1000})
  /usr/local/go/src/net/http/h2_bundle.go:7429 +0x149
bufio.(*Writer).Flush(0xc000596340)
  /usr/local/go/src/bufio/bufio.go:628 +0x62
net/http.(*http2ClientConn).writeHeaders(0xc000660180, 0x9, 0x0, 0x4000, {0xc00066db00?, 0x0?, 0x2403?})
  /usr/local/go/src/net/http/h2_bundle.go:8579 +0x195
net/http.(*http2clientStream).encodeAndWriteHeaders(0xc000acb380, 0xc0007f3900)
  /usr/local/go/src/net/http/h2_bundle.go:8455 +0x38e
net/http.(*http2clientStream).writeRequest(0xc000acb380, 0xc0007f3900)
  /usr/local/go/src/net/http/h2_bundle.go:8343 +0x528
net/http.(*http2clientStream).doRequest(0xc000ac34f0?, 0xc0005bc701?)
  /usr/local/go/src/net/http/h2_bundle.go:8261 +0x1e
created by net/http.(*http2ClientConn).RoundTrip
  /usr/local/go/src/net/http/h2_bundle.go:8190 +0x34a

What's interesting is that the left index is always the same 33554436, if you convert it into hex you will get 0x02000004, which corresponds to write syscall: (SYSCALL_CLASS_UNIX << SYSCALL_CLASS_SHIFT) + 4

Can this be a trampoline messing with memory layout? or some kind of alignment issue?

UPD: Apple Silicon Macs panic as well but with arbitrary left index.

UPD2:
Managed to build minimal repro script, need to be run while VPN client is establishing connection:

package main

import (
	"log"
	"net/http"
	"time"
)

func main() {
	for {
		time.Sleep(500 * time.Millisecond)
		log.Println("hello")
		resp, err := http.Get("https://google.com")
		if err != nil {
			continue
		}
		resp.Body.Close()
	}
}

Disabling HTTP KeepAlives "fixes" the issue.
It seems, VPN client rewrites some network routes and when Go tries to reuse a connection from a pool something in libc or kernel breaks and Write() syscall returns incorrect value.

[bcmills]

Huh. At the very least (*poll.FD).Write should probably validate that n < max - nn and treat the connection as broken.

Even so, we should narrow down whether it is a Go bug or a macOS bug.

• Can you reproduce this same behavior with a program written in C?
• Does the Go reproducer also reproduce the bug in a darwin/amd64 binary?