Fix race between cat /proc/*/wchan and rmmod et al

kallsyms_lookup() can go iterating over modules list unprotected which is OK
for emergency situations (oops), but not OK for regular stuff like
/proc/*/wchan.

Introduce lookup_symbol_name()/lookup_module_symbol_name() which copy symbol
name into caller-supplied buffer or return -ERANGE.  All copying is done with
module_mutex held, so...

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/kernel/module.c b/kernel/module.c
index bf4dccadf7b..3da76ad32d7 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2126,6 +2126,29 @@ const char *module_address_lookup(unsigned long addr,
         return NULL;
 }
 
+int lookup_module_symbol_name(unsigned long addr, char *symname)
+{
+        struct module *mod;
+
+        mutex_lock(&module_mutex);
+        list_for_each_entry(mod, &modules, list) {
+                if (within(addr, mod->module_init, mod->init_size) ||
+                    within(addr, mod->module_core, mod->core_size)) {
+                        const char *sym;
+
+                        sym = get_ksymbol(mod, addr, NULL, NULL);
+                        if (!sym)
+                                goto out;
+                        strlcpy(symname, sym, KSYM_NAME_LEN + 1);
+                        mutex_unlock(&module_mutex);
+                        return 0;
+                }
+        }
+out:
+        mutex_unlock(&module_mutex);
+        return -ERANGE;
+}
+
 int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
                         char *name, char *module_name, int *exported)
 {