Re: grub2 not using linux cmdline as verbatim

[Andrei Borzenkov]

В Thu, 04 Jun 2015 19:24:51 +0200
Jiri Jaburek <address@hidden> пишет:

> Hello,
> the documentation [1] for linux / linux16 mentions that
> 
>   "The rest of the line is passed verbatim as the kernel command-line."
> 
> which is false, I was able to cause
> 
>   error: syntax error.
>   error: Incorrect command.
>   error: syntax error.
> 
> by specifying & (ampersand character) on the command line.
> (Yes, grub2.cfg, not the shell generation logic.)
> 

Like in "normal" shell commands receive arguments after pre-processing
by shell (grub CLI). grub documentation explicitly says that "&" is
metacharacter and needs to be quoted if you want to include it verbatim.

> Quoting the character seems to help, but that further proves that
> grub doesn't treat even the quotes as verbatim text.
> 
> Since I have all this as part of a more complex infrastructure,
> it's impossible to hand-edit every such occurrence - could you please
> tell me which characters have special meaning (aside from newline)
> and/or confirm that the current behavior (not treating text as
> verbatim) is a bug?
> 
> If it is a feature, what would be the easiest way to make grub
> treat unknown (external) kernel cmdline as valid? Quoting the entire
> cmdline (after kernel filename) seems to leave the quotes intact and
> take the cmdline as verbatim, but I don't want the extra quotes to
> be there if I need them to make grub treat the cmdline as verbatim
> in the first place.
> 
> TL;DR:
> 
> - this works:
>   linux16 /somekernel opt1 opt2 opt3
> 
> - this triggers syntax error:
>   linux16 /somekernel opt1 opt2&opt3
> 
> - this works, but removes the quotes:
>   linux16 /somekernel opt1 "opt2&opt3"
> 

Are you surprised that

echo "opt2&opt3"

outputs

opt2&opt3

without quotes?

> - this also works, but leaves the quotes intact:
>   linux16 /somekernel "opt1 opt2&opt3"
> 

Yes, this is a bit magical. GRUB sees space in argument and quotes it
so kernel will correctly parse it as a single word and not split in
multiple arguments. Think about it it as a syntactic sugar which frees
user from using extra quotes like

linux /vmlinuz '"single argument with spaces"'

May be it should be explicitly mentioned in documentation.

> Reproducible with grub-2.02 on x86 and powerpc at least, on
> RHEL/Fedora, but reproduced with Super Grub Disk, so it's not
> downstream-specific.
> 
> Thanks,
> Jiri
> 
> 
> [1]: http://www.gnu.org/software/grub/manual/grub.html#linux
> 
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