module: make module_address_lookup safe

module_address_lookup releases preemption then returns a pointer into
the module space.  The only user (kallsyms) copies the result, so just
do that under the preempt disable.

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

1 files changed, 13 insertions, 9 deletions

diff --git a/kernel/module.c b/kernel/module.c
index 12067ff34d01..e814cd7da634 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2230,14 +2230,13 @@ static const char *get_ksymbol(struct module *mod,
         return mod->strtab + mod->symtab[best].st_name;
 }
 
-/* For kallsyms to ask for address resolution.  NULL means not found.
-   We don't lock, as this is used for oops resolution and races are a
-   lesser concern. */
-/* FIXME: Risky: returns a pointer into a module w/o lock */
-const char *module_address_lookup(unsigned long addr,
-                                  unsigned long *size,
-                                  unsigned long *offset,
-                                  char **modname)
+/* For kallsyms to ask for address resolution.  NULL means not found.  Careful
+ * not to lock to avoid deadlock on oopses, simply disable preemption. */
+char *module_address_lookup(unsigned long addr,
+                            unsigned long *size,
+                            unsigned long *offset,
+                            char **modname,
+                            char *namebuf)
 {
         struct module *mod;
         const char *ret = NULL;
@@ -2252,8 +2251,13 @@ const char *module_address_lookup(unsigned long addr,
                         break;
                 }
         }
+        /* Make a copy in here where it's safe */
+        if (ret) {
+                strncpy(namebuf, ret, KSYM_NAME_LEN - 1);
+                ret = namebuf;
+        }
         preempt_enable();
-        return ret;
+        return (char *)ret;
 }
 
 int lookup_module_symbol_name(unsigned long addr, char *symname)