module: Factor out elf_validity_cache_strtab

This patch only moves the existing strtab population to a function.
Validation comes in a following patch, this is split out to make the new
validation checks more clearly separated.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

Author: maurer

kernel/module/main.c

@@ -2089,6 +2089,23 @@ static int elf_validity_cache_index(struct load_info *info, int flags)
 	return 0;
 }
 
+/**
+ * elf_validity_cache_strtab() - Cache symbol string table
+ * @info: Load info to read from and update.
+ *        Must have &load_info->sechdrs and &load_info->secstrings populated.
+ *        Must have &load_info->index populated.
+ *
+ * Return: 0 on success, negative error code if a check failed.
+ */
+static int elf_validity_cache_strtab(struct load_info *info)
+{
+	Elf_Shdr *str_shdr = &info->sechdrs[info->index.str];
+	char *strtab = (char *)info->hdr + str_shdr->sh_offset;
+
+	info->strtab = strtab;
+	return 0;
+}
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -2122,9 +2139,9 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
 	err = elf_validity_cache_index(info, flags);
 	if (err < 0)
 		return err;
-
-	/* Sets internal strings. */
-	info->strtab = (char *)info->hdr + info->sechdrs[info->index.str].sh_offset;
+	err = elf_validity_cache_strtab(info);
+	if (err < 0)
+		return err;
 
 	/* This is temporary: point mod into copy of data. */
 	info->mod = (void *)info->hdr + info->sechdrs[info->index.mod].sh_offset;