syscall: special case cmd.exe /c <command>
in StartProcess
#69939
Labels
compiler/runtime
Issues related to the Go compiler and/or runtime.
NeedsDecision
Feedback is required from experts, contributors, and/or the community before a change can be made.
OS-Windows
Background
It is well known that os/exec doesn't correctly escape nor quote
*.bat
,*.cmd
,cmd /c *
arguments. This is because in all three cases the escape/quote rules that apply are the ones defined in cmd.exe docs, which are slightly different than the onesos/exec
and syscall.StartProcess follow, defined in parsing-c-command-line-arguments. This discrepancy causes bugs like #1849, #17149, #68313, and can also lead to security vulnerabilities.The only workaround that exists today to reliably execute
*.bat
,*.cmd
,cmd /c *
command usingos/exec
is to manually escape/quote the arguments at caller site and pass the resulting string to syscall.SysProcAttr.CmdLine. The problem is that having a robust implementation is complicated, so projects tend to have half-backed solutions, if any.Proposal
Special case
%COMSPEC% /c <command>
(%COMSPEC% usually points tocmd.exe
) by applying the cmd.exe escape/quote rules to<command>
. The exact rules are left for the implementer, as they are well documented.Some considerations to take into account:
cmd.exe
has two types of quotation rules, let's call it default and special. We should follow the special rule (search for/s
in the docs), as it is 100% predictable in comparison with the default rule, which has many limitations and can easily fallback to the special rule.The special rule is simple: if
<command>
starts with a"
, then the the leading and trailing quotes are stripped. This means that we should always surround<command>
with quotes and pass/s
before/c
.cmd.exe
allows passing multiple cmd-specific parameters before/c
appears. The command is always what goes after/c
. Therefore,cmd.exe /d /c <command>
is valid and we should special-case it.cmd.exe
also execute commands passed after the/k
parameter. That is used to keep the command processor running after the command is executed, so it doesn't really fit well with the one-shot approach ofsyscall.StartProcess
. We can ignore it.Why not special case also bat/cmd files
This proposal doesn't attempt to solve issues related to directly executing bat/cmd scripts for the following reasons:
cmd /c
instead.CreateProcess
recommend to usecmd /c
..bat
and.cmd
files inCommand::new
rust-lang/rust#123728.os/exec
will now have a good workaround to execute bat files:exec.Command("cmd.exe", "/c", "foo.bat", "arg 1")
Note that I'm not putting this proposal in the proposal process because it is not adding new API nor breaking existing behavior. It is more as an umbrella issue to discuss the design and the implementation.
@golang/security @golang/windows
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