From 2a330dba93ff11bc00eda76e9419bc52b0c7ead6 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Fri, 22 Jan 2021 16:07:29 +1100
Subject: [PATCH] lib/arg: Block repeated short options that require an
 argument

Fuzzing found the following crash:

  search -hhhhhhhhhhhhhf

We didn't allocate enough option space for 13 hints because the
allocation code counts the number of discrete arguments (i.e. argc).
However, the shortopt parsing code will happily keep processing
a combination of short options without checking if those short
options require an argument. This means you can easily end writing
past the allocated option space.

This fixes a OOB write which can cause heap corruption.

Fixes: CVE-2021-20225

Reported-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
---
 grub-core/lib/arg.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/grub-core/lib/arg.c b/grub-core/lib/arg.c
index 3288609..537c5e9 100644
--- a/grub-core/lib/arg.c
+++ b/grub-core/lib/arg.c
@@ -299,6 +299,19 @@ grub_arg_parse (grub_extcmd_t cmd, int argc, char **argv,
 		 it can have an argument value.  */
 	      if (*curshort)
 		{
+		  /*
+		   * Only permit further short opts if this one doesn't
+		   * require a value.
+		   */
+		  if (opt->type != ARG_TYPE_NONE &&
+		      !(opt->flags & GRUB_ARG_OPTION_OPTIONAL))
+		    {
+		      grub_error (GRUB_ERR_BAD_ARGUMENT,
+				  N_("missing mandatory option for `%s'"),
+				  opt->longarg);
+		      goto fail;
+		    }
+
 		  if (parse_option (cmd, opt, 0, usr) || grub_errno)
 		    goto fail;
 		}
-- 
2.14.2