module: refactor out section header rewriting

Put all the "rewrite and check section headers" in one place.  This
adds another iteration over the sections, but it's far clearer.  We
iterate once for every find_section() so we already iterate over many
times.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

kernel/module.c

@@ -2158,6 +2158,7 @@ struct load_info {
 	} index;
 };
 
+/* Sets info->hdr and info->len. */
 static int copy_and_check(struct load_info *info, const void __user *umod, unsigned long len)
 {
 	int err;
@@ -2199,6 +2200,39 @@ static int copy_and_check(struct load_info *info, const void __user *umod, unsig
 	return err;
 }
 
+static int rewrite_section_headers(struct load_info *info)
+{
+	unsigned int i;
+
+	/* This should always be true, but let's be sure. */
+	info->sechdrs[0].sh_addr = 0;
+
+	for (i = 1; i < info->hdr->e_shnum; i++) {
+		Elf_Shdr *shdr = &info->sechdrs[i];
+		if (shdr->sh_type != SHT_NOBITS
+		    && info->len < shdr->sh_offset + shdr->sh_size) {
+			printk(KERN_ERR "Module len %lu truncated\n",
+			       info->len);
+			return -ENOEXEC;
+		}
+
+		/* Mark all sections sh_addr with their address in the
+		   temporary image. */
+		shdr->sh_addr = (size_t)info->hdr + shdr->sh_offset;
+
+#ifndef CONFIG_MODULE_UNLOAD
+		/* Don't load .exit sections */
+		if (strstarts(info->secstrings+shdr->sh_name, ".exit"))
+			shdr->sh_flags &= ~(unsigned long)SHF_ALLOC;
+#endif
+		/* Don't keep modinfo and version sections. */
+		if (!strcmp(info->secstrings+shdr->sh_name, "__versions")
+		    || !strcmp(info->secstrings+shdr->sh_name, ".modinfo"))
+			shdr->sh_flags &= ~(unsigned long)SHF_ALLOC;
+	}
+	return 0;
+}
+
 /*
  * Set up our basic convenience variables (pointers to section headers,
  * search for module section index etc), and do some basic section
@@ -2210,33 +2244,27 @@ static int copy_and_check(struct load_info *info, const void __user *umod, unsig
 static struct module *setup_load_info(struct load_info *info)
 {
 	unsigned int i;
+	int err;
 	struct module *mod;
 
 	/* Set up the convenience variables */
 	info->sechdrs = (void *)info->hdr + info->hdr->e_shoff;
-	info->secstrings = (void *)info->hdr + info->sechdrs[info->hdr->e_shstrndx].sh_offset;
-	info->sechdrs[0].sh_addr = 0;
-
-	for (i = 1; i < info->hdr->e_shnum; i++) {
-		if (info->sechdrs[i].sh_type != SHT_NOBITS
-		    && info->len < info->sechdrs[i].sh_offset + info->sechdrs[i].sh_size)
-			goto truncated;
+	info->secstrings = (void *)info->hdr
+		+ info->sechdrs[info->hdr->e_shstrndx].sh_offset;
 
-		/* Mark all sections sh_addr with their address in the
-		   temporary image. */
-		info->sechdrs[i].sh_addr = (size_t)info->hdr + info->sechdrs[i].sh_offset;
+	err = rewrite_section_headers(info);
+	if (err)
+		return ERR_PTR(err);
 
-		/* Internal symbols and strings. */
+	/* Find internal symbols and strings. */
+	for (i = 1; i < info->hdr->e_shnum; i++) {
 		if (info->sechdrs[i].sh_type == SHT_SYMTAB) {
 			info->index.sym = i;
 			info->index.str = info->sechdrs[i].sh_link;
-			info->strtab = (char *)info->hdr + info->sechdrs[info->index.str].sh_offset;
+			info->strtab = (char *)info->hdr
+				+ info->sechdrs[info->index.str].sh_offset;
+			break;
 		}
-#ifndef CONFIG_MODULE_UNLOAD
-		/* Don't load .exit sections */
-		if (strstarts(info->secstrings+info->sechdrs[i].sh_name, ".exit"))
-			info->sechdrs[i].sh_flags &= ~(unsigned long)SHF_ALLOC;
-#endif
 	}
 
 	info->index.mod = find_sec(info->hdr, info->sechdrs, info->secstrings,
@@ -2258,19 +2286,11 @@ static struct module *setup_load_info(struct load_info *info)
 	info->index.info = find_sec(info->hdr, info->sechdrs, info->secstrings, ".modinfo");
 	info->index.pcpu = find_pcpusec(info->hdr, info->sechdrs, info->secstrings);
 
-	/* Don't keep modinfo and version sections. */
-	info->sechdrs[info->index.info].sh_flags &= ~(unsigned long)SHF_ALLOC;
-	info->sechdrs[info->index.vers].sh_flags &= ~(unsigned long)SHF_ALLOC;
-
 	/* Check module struct version now, before we try to use module. */
 	if (!check_modstruct_version(info->sechdrs, info->index.vers, mod))
 		return ERR_PTR(-ENOEXEC);
 
 	return mod;
-
- truncated:
-	printk(KERN_ERR "Module len %lu truncated\n", info->len);
-	return ERR_PTR(-ENOEXEC);
 }
 
 static int check_modinfo(struct module *mod,