[Bug 2112179] Re: Cannot pass unescaped double quotes to the linux command line

[Mate Kukri]

** Changed in: grub2 (Ubuntu)
       Status: New => In Progress

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Title:
  Cannot pass unescaped double quotes to the linux command line

Status in grub2 package in Ubuntu:
  In Progress

Bug description:
  I am writing a `grub.cfg` which contains this:

  ```
      linux /boot/kernel \
          root=/dev/mapper/verity-root \
          dm_mod.create="\"verity-root,,ro,0 163840 verity 1 /dev/vda3 /dev/vda3 4096 4096 10240 10240 sha256 ${ROOT_HASH_A} -\"" \
          ${kernel_common_cmdline}
  ```

  The problem I have is that the kernel then ultimately sees this:

  `dm_mod.create=\"verity-root,,ro,0 163840 verity 1 /dev/vda3 /dev/vda3
  4096 4096 10240 10240 sha256
  4b2693f593b5472ae2661fa9b4a499dce2301e6b66d385d1d7ee8bde1466e87f -\"`

  And not

  `dm_mod.create="verity-root,,ro,0 163840 verity 1 /dev/vda3 /dev/vda3
  4096 4096 10240 10240 sha256
  4b2693f593b5472ae2661fa9b4a499dce2301e6b66d385d1d7ee8bde1466e87f -"`

  as I intended (and what the documentation states should be the result,
  see the paragraph on quoting here:
  https://www.gnu.org/software/grub/manual/grub/html_node/Shell_002dlike-
  scripting.html).

  There are various ways to try and work around the issue, but none result in a command line that the kernel then interprets correctly.
  What appears to be the solution intended by the grub authors gives this result:

  `"dm_mod.create=verity-root,,ro,0 163840 verity 1 /dev/vda3 /dev/vda3
  4096 4096 10240 10240 sha256
  4b2693f593b5472ae2661fa9b4a499dce2301e6b66d385d1d7ee8bde1466e87f -"`

  However the kernel does not parse this correctly.
  One can also try to use escaped spaces to go around the quoting issue, however the backslashes themselves are then automatically escaped by grub in the output, and thus the kernel fails to parse the line correctly too.

  In effect, it is not possible to produce a linux command line that
  contains unescaped double quotes or backslashes, except in the very
  specific way that grub handles the "argument containing a space" case,
  which does not function correctly with the kernel parser.

  This bug is a known issue and patches have been suggested to solve it,
  see here: https://lists.gnu.org/archive/html/grub-
  devel/2023-07/msg00089.html

  This bug is also related to
  https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/445952 but is
  more narrow: my issue is exclusively about grub adding unwanted escape
  characters to the linux command line, not about how it interprets
  quotes coming from environment variables.

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