Fix race between rmmod and cat /proc/kallsyms

module_get_kallsym() leaks "struct module *" outside of module_mutex which is
no-no, because module can dissapear right after mutex unlock.

Copy all needed information from inside module_mutex into caller-supplied
space.

[bunk@stusta.de: is_exported() can now become static]
Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 29 insertions, 34 deletions

diff --git a/include/linux/module.h b/include/linux/module.h
index 799930216626..58d5a10cdf0d 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -370,16 +370,14 @@ struct module *module_text_address(unsigned long addr);
 struct module *__module_text_address(unsigned long addr);
 int is_module_address(unsigned long addr);
 
-/* Returns module and fills in value, defined and namebuf, or NULL if
+/* Returns 0 and fills in value, defined and namebuf, or -ERANGE if
    symnum out of range. */
-struct module *module_get_kallsym(unsigned int symnum, unsigned long *value,
-                                char *type, char *name);
+int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
+                        char *name, char *module_name, int *exported);
 
 /* Look for this name: can be of form module:name. */
 unsigned long module_kallsyms_lookup_name(const char *name);
 
-int is_exported(const char *name, const struct module *mod);
-
 extern void __module_put_and_exit(struct module *mod, long code)
         __attribute__((noreturn));
 #define module_put_and_exit(code) __module_put_and_exit(THIS_MODULE, code);
@@ -527,11 +525,11 @@ static inline const char *module_address_lookup(unsigned long addr,
         return NULL;
 }
 
-static inline struct module *module_get_kallsym(unsigned int symnum,
-                                                unsigned long *value,
-                                                char *type, char *name)
+static inline int module_get_kallsym(unsigned int symnum, unsigned long *value,
+                                        char *type, char *name,
+                                        char *module_name, int *exported)
 {
-        return NULL;
+        return -ERANGE;
 }
 
 static inline unsigned long module_kallsyms_lookup_name(const char *name)
@@ -539,11 +537,6 @@ static inline unsigned long module_kallsyms_lookup_name(const char *name)
         return 0;
 }
 
-static inline int is_exported(const char *name, const struct module *mod)
-{
-        return 0;
-}
-
 static inline int register_module_notifier(struct notifier_block * nb)
 {
         /* no events will happen anyway, so this can always succeed */
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index d086c91d44ed..f1ea6f66ac6c 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -301,25 +301,20 @@ void __print_symbol(const char *fmt, unsigned long address)
 struct kallsym_iter
 {
         loff_t pos;
-        struct module *owner;
         unsigned long value;
         unsigned int nameoff; /* If iterating in core kernel symbols */
         char type;
         char name[KSYM_NAME_LEN+1];
+        char module_name[MODULE_NAME_LEN + 1];
+        int exported;
 };
 
 static int get_ksymbol_mod(struct kallsym_iter *iter)
 {
-        iter->owner = module_get_kallsym(iter->pos - kallsyms_num_syms,
-                                         &iter->value, &iter->type,
-                                         iter->name);
-        if (iter->owner == NULL)
+        if (module_get_kallsym(iter->pos - kallsyms_num_syms, &iter->value,
+                                &iter->type, iter->name, iter->module_name,
+                                &iter->exported) < 0)
                 return 0;
-
-        /* Label it "global" if it is exported, "local" if not exported. */
-        iter->type = is_exported(iter->name, iter->owner)
-                ? toupper(iter->type) : tolower(iter->type);
-
         return 1;
 }
 
@@ -328,7 +323,7 @@ static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
 {
         unsigned off = iter->nameoff;
 
-        iter->owner = NULL;
+        iter->module_name[0] = '\0';
         iter->value = kallsyms_addresses[iter->pos];
 
         iter->type = kallsyms_get_symbol_type(off);
@@ -392,12 +387,17 @@ static int s_show(struct seq_file *m, void *p)
         if (!iter->name[0])
                 return 0;
 
-        if (iter->owner)
+        if (iter->module_name[0]) {
+                char type;
+
+                /* Label it "global" if it is exported,
+                 * "local" if not exported. */
+                type = iter->exported ? toupper(iter->type) :
+                                        tolower(iter->type);
                 seq_printf(m, "%0*lx %c %s\t[%s]\n",
                            (int)(2*sizeof(void*)),
-                           iter->value, iter->type, iter->name,
-                           module_name(iter->owner));
-        else
+                           iter->value, type, iter->name, iter->module_name);
+        } else
                 seq_printf(m, "%0*lx %c %s\n",
                            (int)(2*sizeof(void*)),
                            iter->value, iter->type, iter->name);
diff --git a/kernel/module.c b/kernel/module.c
index 43a529a1fa48..5ee65994a3bc 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1472,7 +1472,7 @@ static void setup_modinfo(struct module *mod, Elf_Shdr *sechdrs,
 }
 
 #ifdef CONFIG_KALLSYMS
-int is_exported(const char *name, const struct module *mod)
+static int is_exported(const char *name, const struct module *mod)
 {
         if (!mod && lookup_symbol(name, __start___ksymtab, __stop___ksymtab))
                 return 1;
@@ -2124,8 +2124,8 @@ const char *module_address_lookup(unsigned long addr,
         return NULL;
 }
 
-struct module *module_get_kallsym(unsigned int symnum, unsigned long *value,
-                                char *type, char *name)
+int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
+                        char *name, char *module_name, int *exported)
 {
         struct module *mod;
 
@@ -2136,13 +2136,15 @@ struct module *module_get_kallsym(unsigned int symnum, unsigned long *value,
                         *type = mod->symtab[symnum].st_info;
                         strlcpy(name, mod->strtab + mod->symtab[symnum].st_name,
                                 KSYM_NAME_LEN + 1);
+                        strlcpy(module_name, mod->name, MODULE_NAME_LEN + 1);
+                        *exported = is_exported(name, mod);
                         mutex_unlock(&module_mutex);
-                        return mod;
+                        return 0;
                 }
                 symnum -= mod->num_symtab;
         }
         mutex_unlock(&module_mutex);
-        return NULL;
+        return -ERANGE;
 }
 
 static unsigned long mod_find_symname(struct module *mod, const char *name)