Stack overflow in UploadPack

[icyphox]

Hi,

I'm running into a stack overflow when plumbing/transport/server.(*upSession).UploadPack gets called. Here's the traceback:

goroutine 3250208 [running]:
github.com/go-git/go-git/v5/storage/filesystem.(*deltaObject).Type(0xc000a61c80?)
        <autogenerated>:1 +0x34 fp=0xc020f20378 sp=0xc020f20370 pc=0x7bbdf4
github.com/go-git/go-git/v5/plumbing/format/packfile.(*deltaSelector).fixAndBreakChainsOne(0x9bb780?, 0xc040f1fc60?, 0xc000abbe60)
        /home/icy/go/pkg/mod/github.com/go-git/go-git/v5@v5.11.0/plumbing/format/packfile/delta_selector.go:152 +0x31 fp=0xc020f203e0 sp=0xc020f20378 pc=0x799971
github.com/go-git/go-git/v5/plumbing/format/packfile.(*deltaSelector).fixAndBreakChainsOne(0x9bb780?, 0xc040f1fc60?, 0xc00060a6c0)
        /home/icy/go/pkg/mod/github.com/go-git/go-git/v5@v5.11.0/plumbing/format/packfile/delta_selector.go:177 +0xc5 fp=0xc020f20448 sp=0xc020f203e0 pc=0x799a05
github.com/go-git/go-git/v5/plumbing/format/packfile.(*deltaSelector).fixAndBreakChainsOne(0x9bb780?, 0xc040f1fc60?, 0xc000abbe60)
        /home/icy/go/pkg/mod/github.com/go-git/go-git/v5@v5.11.0/plumbing/format/packfile/delta_selector.go:177 +0xc5 fp=0xc020f204b0 sp=0xc020f20448 pc=0x799a05
github.com/go-git/go-git/v5/plumbing/format/packfile.(*deltaSelector).fixAndBreakChainsOne(0x9bb780?, 0xc040f1fc60?, 0xc00060a6c0)
        /home/icy/go/pkg/mod/github.com/go-git/go-git/v5@v5.11.0/plumbing/format/packfile/delta_selector.go:177 +0xc5 fp=0xc020f20518 sp=0xc020f204b0 pc=0x799a05

... snip ...

        /home/icy/go/pkg/mod/github.com/go-git/go-git/v5@v5.11.0/plumbing/format/packfile/delta_selector.go:143 +0x17a fp=0xc040f1fd90 sp=0xc040f1fc08 pc=0x7998da
github.com/go-git/go-git/v5/plumbing/format/packfile.(*deltaSelector).objectsToPack(0xc00036da60, {0xc000a80000?, 0x15a3, 0x24f44eb48?}, 0xa)
        /home/icy/go/pkg/mod/github.com/go-git/go-git/v5@v5.11.0/plumbing/format/packfile/delta_selector.go:116 +0x245 fp=0xc040f1fe38 sp=0xc040f1fd90 pc=0x799625
github.com/go-git/go-git/v5/plumbing/format/packfile.(*deltaSelector).ObjectsToPack(0xc00036da60, {0xc000a80000, 0x15a3, 0x1b33}, 0xa)
        /home/icy/go/pkg/mod/github.com/go-git/go-git/v5@v5.11.0/plumbing/format/packfile/delta_selector.go:40 +0x85 fp=0xc040f1ff28 sp=0xc040f1fe38 pc=0x798d85
github.com/go-git/go-git/v5/plumbing/format/packfile.(*Encoder).Encode(0xc0007e4f00, {0xc000a80000?, 0x6d27a8?, 0xc00011a240?}, 0xb42f40?)
        /home/icy/go/pkg/mod/github.com/go-git/go-git/v5@v5.11.0/plumbing/format/packfile/encoder.go:53 +0x36 fp=0xc040f1ff88 sp=0xc040f1ff28 pc=0x79be56
github.com/go-git/go-git/v5/plumbing/transport/server.(*upSession).UploadPack.func1()
        /home/icy/go/pkg/mod/github.com/go-git/go-git/v5@v5.11.0/plumbing/transport/server/server.go:173 +0x31 fp=0xc040f1ffe0 sp=0xc040f1ff88 pc=0x877431
runtime.goexit()
        /usr/local/go/src/runtime/asm_amd64.s:1650 +0x1 fp=0xc040f1ffe8 sp=0xc040f1ffe0 pc=0x46b1c1
created by github.com/go-git/go-git/v5/plumbing/transport/server.(*upSession).UploadPack in goroutine 3250206
        /home/icy/go/pkg/mod/github.com/go-git/go-git/v5@v5.11.0/plumbing/transport/server/server.go:171 +0x456

Any pointers on why this occurs? A cursory peek at the code base and I see a recursive call to fixAndBreakChainsOne here:

go-git/plumbing/format/packfile/delta_selector.go

Line 177 in 302ddde

if err := dw.fixAndBreakChainsOne(objectsToPack, base); err != nil {

[pjbgf]

@icyphox would you be able to provide some steps to reproduce? Is the repository public being used public?

[icyphox]

Hi, reproducing is something I'm struggling with since the cause seems almost magical. It either happens 3–4 times a day or sometimes weeks go by without it crashing. The code is public: https://github.com/icyphox/legit/blob/21627fed77b003cdcb6daa4c682a841184880028/routes/git.go#L95

For what it's worth, the system this is being deployed on is OpenBSD amd64.