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runtime: ignore map size hint if there's not enough memory? #24308

mfrw opened this issue Mar 8, 2018 · 15 comments

runtime: ignore map size hint if there's not enough memory? #24308

mfrw opened this issue Mar 8, 2018 · 15 comments


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@mfrw mfrw commented Mar 8, 2018

Please answer these questions before submitting your issue. Thanks!

What did you do?

go test in encoding/gob

What did you expect to see?

Passed tests

What did you see instead?


Does this issue reproduce with the latest release (go1.10)?


System details

go version devel +0add9a4dcf Thu Mar 8 03:26:22 2018 +0000 linux/amd64
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build389146753=/tmp/go-build -gno-record-gcc-switches"
GOROOT/bin/go version: go version devel +0add9a4dcf Thu Mar 8 03:26:22 2018 +0000 linux/amd64
GOROOT/bin/go tool compile -V: compile version devel +0add9a4dcf Thu Mar 8 03:26:22 2018 +0000
uname -sr: Linux 4.9.20-1-MANJARO
LSB Version:	n/a
Distributor ID:	ManjaroLinux
Description:	Manjaro Linux
Release:	17.0.1
Codename:	Gellivara
/usr/lib/ GNU C Library (GNU libc) stable release version 2.25, by Roland McGrath et al.
gdb --version: GNU gdb (GDB) 7.12.1
=== RUN TestUintCodec --- PASS: TestUintCodec (0.00s) === RUN TestIntCodec --- PASS: TestIntCodec (0.00s) === RUN TestScalarEncInstructions --- PASS: TestScalarEncInstructions (0.00s) === RUN TestScalarDecInstructions --- PASS: TestScalarDecInstructions (0.00s) === RUN TestEndToEnd --- PASS: TestEndToEnd (0.00s) === RUN TestOverflow --- PASS: TestOverflow (0.00s) === RUN TestNesting --- PASS: TestNesting (0.00s) === RUN TestAutoIndirection --- PASS: TestAutoIndirection (0.00s) === RUN TestReorderedFields --- PASS: TestReorderedFields (0.00s) === RUN TestIgnoredFields --- PASS: TestIgnoredFields (0.00s) === RUN TestBadRecursiveType --- PASS: TestBadRecursiveType (0.00s) === RUN TestIndirectSliceMapArray --- PASS: TestIndirectSliceMapArray (0.00s) === RUN TestInterface --- PASS: TestInterface (0.00s) === RUN TestInterfaceBasic --- PASS: TestInterfaceBasic (0.00s) === RUN TestInterfacePointer --- PASS: TestInterfacePointer (0.00s) === RUN TestIgnoreInterface --- PASS: TestIgnoreInterface (0.00s) === RUN TestUnexportedFields --- PASS: TestUnexportedFields (0.00s) === RUN TestDebugSingleton --- PASS: TestDebugSingleton (0.00s) === RUN TestDebugStruct --- PASS: TestDebugStruct (0.00s) === RUN TestFuzz --- PASS: TestFuzz (0.00s) codec_test.go:1424: disabled; run with -gob.fuzz to enable === RUN TestFuzzRegressions --- PASS: TestFuzzRegressions (0.00s) codec_test.go:1444: disabled; run with -gob.fuzz to enable === RUN TestFuzzOneByte fatal error: runtime: out of memory

runtime stack:
runtime.throw(0x5b89e1, 0x16)
/home/mfrw/go/src/runtime/panic.go:617 +0x80
runtime.sysMap(0xc004000000, 0xdd00000000, 0x6be7f8)
/home/mfrw/go/src/runtime/mem_linux.go:156 +0xc7
runtime.(*mheap).sysAlloc(0x6a48e0, 0xdd00000000, 0x80, 0x0)
/home/mfrw/go/src/runtime/malloc.go:601 +0x1d0
runtime.(*mheap).grow(0x6a48e0, 0x6e80000, 0x0)
/home/mfrw/go/src/runtime/mheap.go:920 +0x42
runtime.(*mheap).allocSpanLocked(0x6a48e0, 0x6e80000, 0x6be808, 0x7f98353cbdd0)
/home/mfrw/go/src/runtime/mheap.go:848 +0x337
runtime.(*mheap).alloc_m(0x6a48e0, 0x6e80000, 0xffffffffffff0100, 0x7f98353cbe08)
/home/mfrw/go/src/runtime/mheap.go:692 +0x119
/home/mfrw/go/src/runtime/mheap.go:759 +0x4d
runtime.(*mheap).alloc(0x6a48e0, 0x6e80000, 0x7f9835010100, 0x4157f9)
/home/mfrw/go/src/runtime/mheap.go:758 +0x8a
runtime.largeAlloc(0xdd00000000, 0xc000280001, 0x7f9838545000)
/home/mfrw/go/src/runtime/malloc.go:1001 +0x94
/home/mfrw/go/src/runtime/malloc.go:896 +0x46
/home/mfrw/go/src/runtime/asm_amd64.s:403 +0x66

goroutine 27 [running]:
/home/mfrw/go/src/runtime/asm_amd64.s:363 fp=0xc000287748 sp=0xc000287740 pc=0x455360
runtime.mallocgc(0xdd00000000, 0x5970e0, 0xc0003f2b01, 0xc000287828)
/home/mfrw/go/src/runtime/malloc.go:895 +0x895 fp=0xc0002877e8 sp=0xc000287748 pc=0x40bd45
runtime.newarray(0x5970e0, 0x110000000, 0x5a6da0)
/home/mfrw/go/src/runtime/malloc.go:1030 +0x6a fp=0xc000287818 sp=0xc0002877e8 pc=0x40c12a
runtime.makeBucketArray(0x57f520, 0xc0003edc20, 0xc000376318, 0x5)
/home/mfrw/go/src/runtime/map.go:881 +0xe2 fp=0xc000287850 sp=0xc000287818 pc=0x40e672
runtime.makemap(0x57f520, 0x36f6e6502, 0xc0003edc20, 0x194)
/home/mfrw/go/src/runtime/map.go:328 +0xe3 fp=0xc000287890 sp=0xc000287850 pc=0x40cd53
reflect.makemap(0x57f520, 0x36f6e6502, 0x15)
/home/mfrw/go/src/runtime/map.go:1190 +0x167 fp=0xc0002878c8 sp=0xc000287890 pc=0x40f317
reflect.MakeMapWithSize(0x5dc640, 0x57f520, 0x36f6e6502, 0x1, 0x676e69646f636e65, 0x546e4f2e626f672f)
/home/mfrw/go/src/reflect/value.go:2136 +0x69 fp=0xc0002878f0 sp=0xc0002878c8 pc=0x498899
encoding/gob.(*Decoder).decodeMap(0xc000376300, 0x5dc640, 0x57f520, 0xc000142820, 0x57f520, 0xc0003be3b0, 0x195, 0x5c16e8, 0x5c16a8, 0x5da720, ...)
/home/mfrw/go/src/encoding/gob/decode.go:562 +0x6a9 fp=0xc0002879f8 sp=0xc0002878f0 pc=0x50a1e9
encoding/gob.(*Decoder).decOpFor.func2(0xc00021af50, 0xc000142820, 0x57f520, 0xc0003be3b0, 0x195)
/home/mfrw/go/src/encoding/gob/decode.go:829 +0x97 fp=0xc000287a60 sp=0xc0002879f8 pc=0x544ad7
encoding/gob.(*Decoder).decodeStruct(0xc000376300, 0xc000142a00, 0x5a63a0, 0xc0003be360, 0x199)
/home/mfrw/go/src/encoding/gob/decode.go:471 +0xc7 fp=0xc000287ae8 sp=0xc000287a60 pc=0x508fd7
encoding/gob.(*Decoder).decodeValue(0xc000376300, 0x62, 0x566a80, 0xc0003be360, 0x16)
/home/mfrw/go/src/encoding/gob/decode.go:1205 +0x266 fp=0xc000287b90 sp=0xc000287ae8 pc=0x50f776
encoding/gob.(*Decoder).DecodeValue(0xc000376300, 0x566a80, 0xc0003be360, 0x16, 0x0, 0x0)
/home/mfrw/go/src/encoding/gob/decoder.go:212 +0x134 fp=0xc000287bc8 sp=0xc000287b90 pc=0x510ac4
encoding/gob.(*Decoder).Decode(0xc000376300, 0x566a80, 0xc0003be360, 0xc000287cc8, 0xc000287cb0)
/home/mfrw/go/src/encoding/gob/decoder.go:187 +0x18b fp=0xc000287c30 sp=0xc000287bc8 pc=0x5108eb
encoding/gob.TestFuzzOneByte.func1(0xc0000c14a0, 0xc000287cc8, 0xc000287cb0, 0xc0003bc6c0, 0x112, 0x120, 0xc0003be360)
/home/mfrw/go/src/encoding/gob/codec_test.go:1499 +0xe0 fp=0xc000287c68 sp=0xc000287c30 pc=0x545950
/home/mfrw/go/src/encoding/gob/codec_test.go:1501 +0x630 fp=0xc000287fa8 sp=0xc000287c68 pc=0x52ff50
testing.tRunner(0xc0000c14a0, 0x5c13a8)
/home/mfrw/go/src/testing/testing.go:788 +0xc3 fp=0xc000287fd0 sp=0xc000287fa8 pc=0x4c2183
/home/mfrw/go/src/runtime/asm_amd64.s:1379 +0x1 fp=0xc000287fd8 sp=0xc000287fd0 pc=0x457431
created by testing.(*T).Run
/home/mfrw/go/src/testing/testing.go:835 +0x2c5

goroutine 1 [chan receive]:
testing.(*T).Run(0xc0000c14a0, 0x5b653c, 0xf, 0x5c13a8, 0x46d301)
/home/mfrw/go/src/testing/testing.go:836 +0x2ec
/home/mfrw/go/src/testing/testing.go:1078 +0x64
testing.tRunner(0xc0000c0000, 0xc000057df8)
/home/mfrw/go/src/testing/testing.go:788 +0xc3
testing.runTests(0xc00000c7e0, 0x69d6a0, 0x5c, 0x5c, 0x40b7a1)
/home/mfrw/go/src/testing/testing.go:1076 +0x2a1
testing.(*M).Run(0xc0000be000, 0x0)
/home/mfrw/go/src/testing/testing.go:993 +0x165
_testmain.go:260 +0x13d
exit status 2
FAIL encoding/gob 0.698s

@andybons andybons added this to the Go1.11 milestone Mar 8, 2018
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@andybons andybons commented Mar 8, 2018

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@0xmohit 0xmohit commented Mar 8, 2018

git bisect points to 2b41554.

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@mvdan mvdan commented Mar 8, 2018

@mfrw could you provide information about your hardware, such as the memory size and if you use any swap? None of the builders seem to have seen this panic, so maybe it's got something to do with the machine.

Also, is it just a flake, or does it happen every single time you run go test?

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@mfrw mfrw commented Mar 8, 2018

@mvdan My ram is 8 Gb and yes I do use swap (8 Gb).
No, I think its something weird, it passes all.bash but when I go inside the encode/gob package and test, it breaks.
NOTE: It did not break on go1.10.
Btw I tried to test it on my mac and it still broke.

=== RUN   TestFuzzRegressions
--- PASS: TestFuzzRegressions (0.00s)
        codec_test.go:1444: disabled; run with -gob.fuzz to enable
=== RUN   TestFuzzOneByte
signal: killed
FAIL    encoding/gob    65.392s
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@mvdan mvdan commented Mar 8, 2018

Actually, I can reproduce it too on my linux laptop with 8GB of memory and no swap.

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@mvdan mvdan commented Mar 8, 2018

The problem seems to be that the decoder ends up calling reflect.MakeMapWithSize with a size of 14754407682. Which can explain why the runtime then fails to allocate this much memory.

But what I don't understand is why @aclements' change to the runtime makes it suddenly fail. I also don't understand what happened earlier with such a large map creation.

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@josharian josharian commented Mar 8, 2018

Somewhat related: #20221

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@mvdan mvdan commented Mar 8, 2018

I'll send a CL now skipping this index, pending a proper fix in either runtime or gob.

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@gopherbot gopherbot commented Mar 8, 2018

Change mentions this issue: encoding/gob: work around TestFuzzOneByte panic

gopherbot pushed a commit that referenced this issue Mar 9, 2018
The index 248 results in the decoder calling reflect.MakeMapWithSize
with a size of 14754407682 - just under 15GB - which ends up in a
runtime out of memory panic after some recent runtime changes on
machines with 8GB of memory.

Until that is fixed in either runtime or gob, skip the troublesome

Updates #24308.

Change-Id: Ia450217271c983e7386ba2f3f88c9ba50aa346f4
Run-TryBot: Daniel Martí <>
TryBot-Result: Gobot Gobot <>
Reviewed-by: Ian Lance Taylor <>
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@mvdan mvdan commented Mar 9, 2018

The test is passing on my machine now, with the test case being skipped. @aclements, would you like to keep this issue open to investigate if there's anything to fix in the runtime? If not, we can simply keep @josharian's previous issue to decide whether or not the gob package should handle malicious input gracefully.

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@bradfitz bradfitz commented Jun 7, 2018

To summarize, the open question is whether the runtime should ignore the map size hint if there's not enough memory to allocate it:

$ cat map.go 
package main

func main() {
        m := make(map[string]string, 14754407682)

$ go run map.go
fatal error: runtime: out of memory

runtime stack:
runtime.throw(0x46db4e, 0x16)
        /home/bradfitz/go/src/runtime/panic.go:589 +0x6a
runtime.sysMap(0xc004000000, 0x12100000000, 0x4d6bb8)
        /home/bradfitz/go/src/runtime/mem_linux.go:156 +0xc7
runtime.(*mheap).sysAlloc(0x4be660, 0x12100000000, 0x0, 0x7fffca2fd298)
        /home/bradfitz/go/src/runtime/malloc.go:611 +0x1c7
runtime.(*mheap).grow(0x4be660, 0x9080000, 0x0)
        /home/bradfitz/go/src/runtime/mheap.go:920 +0x42
runtime.(*mheap).allocSpanLocked(0x4be660, 0x9080000, 0x4d6bc8, 0x20300000000000)
        /home/bradfitz/go/src/runtime/mheap.go:848 +0x337
runtime.(*mheap).alloc_m(0x4be660, 0x9080000, 0x410100, 0x7fa22a673a00)
        /home/bradfitz/go/src/runtime/mheap.go:692 +0x119
        /home/bradfitz/go/src/runtime/mheap.go:759 +0x4c
runtime.(*mheap).alloc(0x4be660, 0x9080000, 0x7fffca010100, 0x40fef5)
        /home/bradfitz/go/src/runtime/mheap.go:758 +0x8a
runtime.largeAlloc(0x12100000000, 0x440001, 0x7fa22c880000)
        /home/bradfitz/go/src/runtime/malloc.go:1011 +0x97
        /home/bradfitz/go/src/runtime/malloc.go:906 +0x46
        /home/bradfitz/go/src/runtime/asm_amd64.s:351 +0x66

goroutine 1 [running]:
        /home/bradfitz/go/src/runtime/asm_amd64.s:311 fp=0xc0000345e0 sp=0xc0000345d8 pc=0x446640
runtime.mallocgc(0x12100000000, 0x463400, 0x444001, 0x7fa22c880000)
        /home/bradfitz/go/src/runtime/malloc.go:905 +0x896 fp=0xc000034680 sp=0xc0000345e0 pc=0x409f06
runtime.newarray(0x463400, 0x110000000, 0xf)
        /home/bradfitz/go/src/runtime/malloc.go:1040 +0x6a fp=0xc0000346b0 sp=0xc000034680 pc=0x40a27a
runtime.makeBucketArray(0x45c5e0, 0x20, 0x0, 0x0, 0x4ba3a0)
        /home/bradfitz/go/src/runtime/map.go:355 +0x184 fp=0xc0000346e8 sp=0xc0000346b0 pc=0x40b064
runtime.makemap(0x45c5e0, 0x36f6e6502, 0xc000034758, 0xc000074058)
        /home/bradfitz/go/src/runtime/map.go:321 +0xec fp=0xc000034730 sp=0xc0000346e8 pc=0x40adcc
        /home/bradfitz/map.go:4 +0x5c fp=0xc000034798 sp=0xc000034730 pc=0x44e55c
        /home/bradfitz/go/src/runtime/proc.go:201 +0x207 fp=0xc0000347e0 sp=0xc000034798 pc=0x4237e7
        /home/bradfitz/go/src/runtime/asm_amd64.s:1333 +0x1 fp=0xc0000347e8 sp=0xc0000347e0 pc=0x448591
exit status 2

@aclements, @randall77, is this cool?

@bradfitz bradfitz changed the title encoding/gob: test failure for TestFuzzOneByte (runtime: out of memory) runtime: ignore map size hint if there's not enough memory? Jun 7, 2018
@bradfitz bradfitz modified the milestones: Go1.11, Go1.12 Jun 7, 2018
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@ianlancetaylor ianlancetaylor commented Jun 7, 2018

We've agreed in the past that the hint passed to make for a map is only a hint. If we can't allocate enough memory to satisfy the hint, we should ignore it. See #19926. So this is a bug.

@ianlancetaylor ianlancetaylor modified the milestones: Go1.12, Go1.11 Jun 7, 2018
@gopherbot gopherbot removed the NeedsDecision label Jun 7, 2018
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@martisch martisch commented Jun 7, 2018

If its decided to make map buckets not allocate due to insufficient ram it would be nice to allow this check to be not enforced for small maps. e.g. up to 64 elements and for stack allocated buckets for performance (small local maps) and implementation complexity. Also if maps are small and allocation would fail its more likely another allocation might fail soon which cant be avoided.

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@randall77 randall77 commented Jun 8, 2018

@ianlancetaylor I don't think that's what we decided. Reading over the comments on CL 40854, we only prevent panics for obviously bad hints (negative hints, or those which would require allocations larger than the max heap).

We discussed this today. We decided that we should never panic() because of a bad hint, but out of memory is ok. As a practical matter, that means

  1. if hint < 0 { hint = 0 }
  2. if computing the malloc size overflows an int64, or _MaxMem, set hint = 0.
    (take newarray's logic and copy it into hinit, replacing panic with hint=0)
  3. proceed as before
    Those who are really passing adversarial data as a hint need to sanitize it first. It seems hard to sanitize the hint inside the map implementation in the general case.
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@ianlancetaylor ianlancetaylor commented Jun 8, 2018

@randall77 Huh, I guess I misremember. So in that case, this is a bug in encoding/gob?

I understand that it is hard to handle a very large hint in the runtime, but it's even harder to handle in packages outside the runtime. I see that I tried to argue that in the CL also. If I was in the discussion you mention, I've forgotten about it.

@martisch martisch modified the milestones: Go1.11, Unplanned Jun 20, 2018
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