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>

diff --git a/grub-core/lib/arg.c b/grub-core/lib/arg.c
index 8439a0062ff3df224176018fb2a6a145a9f67255..ade82d5dc15c9b929a753788f2d355b2c12bd09e 100644 (file)
--- 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;
                }