[PATCH 08/12] module: Factor out elf_validity_cache_index_str

[Matthew Maurer]

Pull out index validation for the symbol string section.

Note that this does not validate the *contents* of the string table,
only shape and presence of the section.

Signed-off-by: Matthew Maurer <mmau...@google.com>
---
 kernel/module/main.c | 37 ++++++++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 955746649f37..a6bed293d97b 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2047,6 +2047,31 @@ static int elf_validity_cache_index_sym(struct load_info 
*info)
        return 0;
 }
 
+/**
+ * elf_validity_cache_index_str() - Validate and cache strtab index
+ * @info: Load info to cache strtab index in.
+ *        Must have &load_info->sechdrs and &load_info->secstrings populated.
+ *        Must have &load_info->index.sym populated.
+ *
+ * Looks at the symbol table's associated string table, makes sure it is
+ * in-bounds, and caches it.
+ *
+ * Return: %0 if valid, %-ENOEXEC on failure.
+ */
+static int elf_validity_cache_index_str(struct load_info *info)
+{
+       unsigned int str_idx = info->sechdrs[info->index.sym].sh_link;
+
+       if (str_idx == SHN_UNDEF || str_idx >= info->hdr->e_shnum) {
+               pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= 
hdr->e_shnum(%d)\n",
+                      str_idx, str_idx, info->hdr->e_shnum);
+               return -ENOEXEC;
+       }
+
+       info->index.str = str_idx;
+       return 0;
+}
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -2070,7 +2095,6 @@ static int elf_validity_cache_index_sym(struct load_info 
*info)
 static int elf_validity_cache_copy(struct load_info *info, int flags)
 {
        int err;
-       int str_idx;
 
        err = elf_validity_cache_sechdrs(info);
        if (err < 0)
@@ -2087,16 +2111,11 @@ static int elf_validity_cache_copy(struct load_info 
*info, int flags)
        err = elf_validity_cache_index_sym(info);
        if (err < 0)
                return err;
-
-       str_idx = info->sechdrs[info->index.sym].sh_link;
-       if (str_idx == SHN_UNDEF || str_idx >= info->hdr->e_shnum) {
-               pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= 
hdr->e_shnum(%d)\n",
-                               str_idx, str_idx, info->hdr->e_shnum);
-               return -ENOEXEC;
-       }
+       err = elf_validity_cache_index_str(info);
+       if (err < 0)
+               return err;
 
        /* Sets internal strings. */
-       info->index.str = str_idx;
        info->strtab = (char *)info->hdr + 
info->sechdrs[info->index.str].sh_offset;
 
        /* This is temporary: point mod into copy of data. */
-- 
2.47.0.rc1.288.g06298d1525-goog