modules: Fix module_bug_list list corruption race

With all the recent module loading cleanups, we've minimized the code
that sits under module_mutex, fixing various deadlocks and making it
possible to do most of the module loading in parallel.

However, that whole conversion totally missed the rather obscure code
that adds a new module to the list for BUG() handling.  That code was
doubly obscure because (a) the code itself lives in lib/bugs.c (for
dubious reasons) and (b) it gets called from the architecture-specific
"module_finalize()" rather than from generic code.

Calling it from arch-specific code makes no sense what-so-ever to begin
with, and is now actively wrong since that code isn't protected by the
module loading lock any more.

So this commit moves the "module_bug_{finalize,cleanup}()" calls away
from the arch-specific code, and into the generic code - and in the
process protects it with the module_mutex so that the list operations
are now safe.

Future fixups:
 - move the module list handling code into kernel/module.c where it
   belongs.
 - get rid of 'module_bug_list' and just use the regular list of modules
   (called 'modules' - imagine that) that we already create and maintain
   for other reasons.

Reported-and-tested-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Adrian Bunk <bunk@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/avr32/kernel/module.c

@@ -314,10 +314,9 @@ int module_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
 	vfree(module->arch.syminfo);
 	module->arch.syminfo = NULL;
 
-	return module_bug_finalize(hdr, sechdrs, module);
+	return 0;
 }
 
 void module_arch_cleanup(struct module *module)
 {
-	module_bug_cleanup(module);
 }

arch/h8300/kernel/module.c

@@ -112,10 +112,9 @@ int module_finalize(const Elf_Ehdr *hdr,
 		    const Elf_Shdr *sechdrs,
 		    struct module *me)
 {
-	return module_bug_finalize(hdr, sechdrs, me);
+	return 0;
 }
 
 void module_arch_cleanup(struct module *mod)
 {
-	module_bug_cleanup(mod);
 }

arch/mn10300/kernel/module.c

@@ -206,13 +206,12 @@ int module_finalize(const Elf_Ehdr *hdr,
 		    const Elf_Shdr *sechdrs,
 		    struct module *me)
 {
-	return module_bug_finalize(hdr, sechdrs, me);
+	return 0;
 }
 
 /*
  * finish clearing the module
  */
 void module_arch_cleanup(struct module *mod)
 {
-	module_bug_cleanup(mod);
 }

arch/parisc/kernel/module.c

@@ -941,11 +941,10 @@ int module_finalize(const Elf_Ehdr *hdr,
 	nsyms = newptr - (Elf_Sym *)symhdr->sh_addr;
 	DEBUGP("NEW num_symtab %lu\n", nsyms);
 	symhdr->sh_size = nsyms * sizeof(Elf_Sym);
-	return module_bug_finalize(hdr, sechdrs, me);
+	return 0;
 }
 
 void module_arch_cleanup(struct module *mod)
 {
 	deregister_unwind_table(mod);
-	module_bug_cleanup(mod);
 }

arch/powerpc/kernel/module.c

@@ -65,10 +65,6 @@ int module_finalize(const Elf_Ehdr *hdr,
 	const Elf_Shdr *sect;
 	int err;
 
-	err = module_bug_finalize(hdr, sechdrs, me);
-	if (err)
-		return err;
-
 	/* Apply feature fixups */
 	sect = find_section(hdr, sechdrs, "__ftr_fixup");
 	if (sect != NULL)
@@ -101,5 +97,4 @@ int module_finalize(const Elf_Ehdr *hdr,
 
 void module_arch_cleanup(struct module *mod)
 {
-	module_bug_cleanup(mod);
 }

arch/s390/kernel/module.c

@@ -407,10 +407,9 @@ int module_finalize(const Elf_Ehdr *hdr,
 {
 	vfree(me->arch.syminfo);
 	me->arch.syminfo = NULL;
-	return module_bug_finalize(hdr, sechdrs, me);
+	return 0;
 }
 
 void module_arch_cleanup(struct module *mod)
 {
-	module_bug_cleanup(mod);
 }

arch/sh/kernel/module.c

@@ -149,13 +149,11 @@ int module_finalize(const Elf_Ehdr *hdr,
 	int ret = 0;
 
 	ret |= module_dwarf_finalize(hdr, sechdrs, me);
-	ret |= module_bug_finalize(hdr, sechdrs, me);
 
 	return ret;
 }
 
 void module_arch_cleanup(struct module *mod)
 {
-	module_bug_cleanup(mod);
 	module_dwarf_cleanup(mod);
 }

arch/x86/kernel/module.c

@@ -239,11 +239,10 @@ int module_finalize(const Elf_Ehdr *hdr,
 		apply_paravirt(pseg, pseg + para->sh_size);
 	}
 
-	return module_bug_finalize(hdr, sechdrs, me);
+	return 0;
 }
 
 void module_arch_cleanup(struct module *mod)
 {
 	alternatives_smp_module_del(mod);
-	module_bug_cleanup(mod);
 }

include/linux/module.h

@@ -686,17 +686,16 @@ extern int module_sysfs_initialized;
 
 
 #ifdef CONFIG_GENERIC_BUG
-int  module_bug_finalize(const Elf_Ehdr *, const Elf_Shdr *,
+void module_bug_finalize(const Elf_Ehdr *, const Elf_Shdr *,
 			 struct module *);
 void module_bug_cleanup(struct module *);
 
 #else	/* !CONFIG_GENERIC_BUG */
 
-static inline int  module_bug_finalize(const Elf_Ehdr *hdr,
+static inline void module_bug_finalize(const Elf_Ehdr *hdr,
 					const Elf_Shdr *sechdrs,
 					struct module *mod)
 {
-	return 0;
 }
 static inline void module_bug_cleanup(struct module *mod) {}
 #endif	/* CONFIG_GENERIC_BUG */

kernel/module.c

@@ -1537,6 +1537,7 @@ static int __unlink_module(void *_mod)
 {
 	struct module *mod = _mod;
 	list_del(&mod->list);
+	module_bug_cleanup(mod);
 	return 0;
 }
 
@@ -2625,6 +2626,7 @@ static struct module *load_module(void __user *umod,
 	if (err < 0)
 		goto ddebug;
 
+	module_bug_finalize(info.hdr, info.sechdrs, mod);
 	list_add_rcu(&mod->list, &modules);
 	mutex_unlock(&module_mutex);
 
@@ -2650,6 +2652,8 @@ static struct module *load_module(void __user *umod,
 	mutex_lock(&module_mutex);
 	/* Unlink carefully: kallsyms could be walking list. */
 	list_del_rcu(&mod->list);
+	module_bug_cleanup(mod);
+
  ddebug:
 	if (!mod->taints)
 		dynamic_debug_remove(info.debug);

lib/bug.c

@@ -72,8 +72,8 @@ static const struct bug_entry *module_find_bug(unsigned long bugaddr)
 	return NULL;
 }
 
-int module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
-			struct module *mod)
+void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
+			 struct module *mod)
 {
 	char *secstrings;
 	unsigned int i;
@@ -97,8 +97,6 @@ int module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
 	 * could potentially lead to deadlock and thus be counter-productive.
 	 */
 	list_add(&mod->bug_list, &module_bug_list);
-
-	return 0;
 }
 
 void module_bug_cleanup(struct module *mod)