module: fix out-by-one error in kallsyms

Masaki found and patched a kallsyms issue: the last symbol in a
module's symtab wasn't transferred.  This is because we manually copy
the zero'th entry (which is always empty) then copy the rest in a loop
starting at 1, though from src[0].  His fix was minimal, I prefer to
rewrite the loops in more standard form.

There are two loops: one to get the size, and one to copy.  Make these
identical: always count entry 0 and any defined symbol in an allocated
non-init section.

This bug exists since the following commit was introduced.
   module: reduce symbol table for loaded modules (v2)
   commit: 4a4962263f07d14660849ec134ee42b63e95ea9a

LKML: http://lkml.org/lkml/2012/10/24/27
Reported-by: Masaki Kimura <masaki.kimura.kz@hitachi.com>
Cc: stable@kernel.org

diff --git a/kernel/module.c b/kernel/module.c
index 6085f5ef88eaf1fd95159f3db724b16cf43b54d3..6e48c3a43599b6f5d5ce074ec2fbbf8778680ee4 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2293,12 +2293,17 @@ static void layout_symtab(struct module *mod, struct load_info *info)
        src = (void *)info->hdr + symsect->sh_offset;
        nsrc = symsect->sh_size / sizeof(*src);
 
+       /* strtab always starts with a nul, so offset 0 is the empty string. */
+       strtab_size = 1;
+
        /* Compute total space required for the core symbols' strtab. */
-       for (ndst = i = strtab_size = 1; i < nsrc; ++i, ++src)
-               if (is_core_symbol(src, info->sechdrs, info->hdr->e_shnum)) {
-                       strtab_size += strlen(&info->strtab[src->st_name]) + 1;
+       for (ndst = i = 0; i < nsrc; i++) {
+               if (i == 0 ||
+                   is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum)) {
+                       strtab_size += strlen(&info->strtab[src[i].st_name])+1;
                        ndst++;
                }
+       }
 
        /* Append room for core symbols at end of core part. */
        info->symoffs = ALIGN(mod->core_size, symsect->sh_addralign ?: 1);
@@ -2332,15 +2337,15 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
        mod->core_symtab = dst = mod->module_core + info->symoffs;
        mod->core_strtab = s = mod->module_core + info->stroffs;
        src = mod->symtab;
-       *dst = *src;
        *s++ = 0;
-       for (ndst = i = 1; i < mod->num_symtab; ++i, ++src) {
-               if (!is_core_symbol(src, info->sechdrs, info->hdr->e_shnum))
-                       continue;
-
-               dst[ndst] = *src;
-               dst[ndst++].st_name = s - mod->core_strtab;
-               s += strlcpy(s, &mod->strtab[src->st_name], KSYM_NAME_LEN) + 1;
+       for (ndst = i = 0; i < mod->num_symtab; i++) {
+               if (i == 0 ||
+                   is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum)) {
+                       dst[ndst] = src[i];
+                       dst[ndst++].st_name = s - mod->core_strtab;
+                       s += strlcpy(s, &mod->strtab[src[i].st_name],
+                                    KSYM_NAME_LEN) + 1;
+               }
        }
        mod->core_num_syms = ndst;
 }