[PATCH v3] Race between cat /proc/kallsyms and rmmod

[Alexey Dobriyan <adobriyan@sw.ru>]

Iterating code of /proc/kallsyms calls module_get_kallsym() which grabs
and drops module_mutex internally and returns "struct module *",
module is removed, aforementioned "struct module *" is used in non-trivial
way.

Steps to reproduce:

	modprobe/rmmod loop
	cat /proc/kallsyms >/dev/null loop

Copy all needed info under module_mutex.

NOTE: this patch keeps module_mutex static.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
---

 include/linux/module.h |   13 +++++++++----
 kernel/kallsyms.c      |   32 +++++++++++++++++---------------
 kernel/module.c        |   12 ++++++++----
 3 files changed, 34 insertions(+), 23 deletions(-)

--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -370,10 +370,12 @@ struct module *module_text_address(unsig
 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, size_t namelen);
+int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
+			char *name, size_t namelen,
+			char *module_name, size_t module_namelen,
+			int *exported);
 
 /* Look for this name: can be of form module:name. */
 unsigned long module_kallsyms_lookup_name(const char *name);
@@ -530,7 +532,10 @@ static inline const char *module_address
 static inline struct module *module_get_kallsym(unsigned int symnum,
 						unsigned long *value,
 						char *type, char *name,
-						size_t namelen)
+						size_t namelen,
+						char *module_name,
+						size_t module_namelen,
+						int *exported)
 {
 	return NULL;
 }
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -295,25 +295,22 @@ void __print_symbol(const char *fmt, uns
 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, sizeof(iter->name));
-	if (iter->owner == NULL)
+	if (module_get_kallsym(iter->pos - kallsyms_num_syms,
+				 &iter->value, &iter->type,
+				 iter->name, sizeof(iter->name),
+				 iter->module_name, sizeof(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;
 }
 
@@ -322,7 +319,7 @@ static unsigned long get_ksymbol_core(st
 {
 	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);
@@ -386,12 +383,17 @@ static int s_show(struct seq_file *m, vo
 	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);
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2119,8 +2119,10 @@ const char *module_address_lookup(unsign
 	return NULL;
 }
 
-struct module *module_get_kallsym(unsigned int symnum, unsigned long *value,
-				char *type, char *name, size_t namelen)
+int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
+			char *name, size_t namelen,
+			char *module_name, size_t module_namelen,
+			int *exported)
 {
 	struct module *mod;
 
@@ -2131,13 +2133,15 @@ struct module *module_get_kallsym(unsign
 			*type = mod->symtab[symnum].st_info;
 			strlcpy(name, mod->strtab + mod->symtab[symnum].st_name,
 				namelen);
+			strlcpy(module_name, mod->name, module_namelen);
+			*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)