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commands/menuentry: Fix quoting in setparams_prefix()

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Commit 9acdcbf32542 (use single quotes in menuentry setparams command)
says that expressing a quoted single quote will require 3 characters. It
actually requires (and always did require!) 4 characters:

  str: a'b => a'\''b
  len:  3  => 6 (2 for the letters + 4 for the quote)

This leads to not allocating enough memory and thus out of bounds writes
that have been observed to cause heap corruption.

Allocate 4 bytes for each single quote.

Commit 22e7dbb2bb81 (Fix quoting in legacy parser.) does the same
quoting, but it adds 3 as extra overhead on top of the single byte that
the quote already needs. So it's correct.

Fixes: 9acdcbf32542 (use single quotes in menuentry setparams command)
Fixes: CVE-2021-20233

Reported-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Daniel Axtens 2021-01-22 17:10:48 +11:00 committed by Daniel Kiper
parent 0a05f88e2b
commit 2f533a89a8
1 changed files with 1 additions and 1 deletions
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2
grub-core/commands/menuentry.c
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@ -230,7 +230,7 @@ setparams_prefix (int argc, char **args)
len += 3; /* 3 = 1 space + 2 quotes */
p = args[i];
while (*p)
len += (*p++ == '\'' ? 3 : 1);
len += (*p++ == '\'' ? 4 : 1);
}
result = grub_malloc (len + 2);