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>

2 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index 3e3b92dabe3b..ae0117a95cfd 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -30,6 +30,8 @@ extern int sprint_symbol(char *buffer, unsigned long address);
 /* Look up a kernel symbol and print it to the kernel messages. */
 extern void __print_symbol(const char *fmt, unsigned long address);
 
+int lookup_symbol_name(unsigned long addr, char *symname);
+
 #else /* !CONFIG_KALLSYMS */
 
 static inline unsigned long kallsyms_lookup_name(const char *name)
@@ -58,6 +60,11 @@ static inline int sprint_symbol(char *buffer, unsigned long addr)
         return 0;
 }
 
+static inline int lookup_symbol_name(unsigned long addr, char *symname)
+{
+        return -ERANGE;
+}
+
 /* Stupid that this does nothing, but I didn't create this mess. */
 #define __print_symbol(fmt, addr)
 #endif /*CONFIG_KALLSYMS*/
diff --git a/include/linux/module.h b/include/linux/module.h
index 58d5a10cdf0d..099ae5932c68 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -454,6 +454,7 @@ const char *module_address_lookup(unsigned long addr,
                                   unsigned long *symbolsize,
                                   unsigned long *offset,
                                   char **modname);
+int lookup_module_symbol_name(unsigned long addr, char *symname);
 
 /* For extable.c to search modules' exception tables. */
 const struct exception_table_entry *search_module_extables(unsigned long addr);
@@ -525,6 +526,11 @@ static inline const char *module_address_lookup(unsigned long addr,
         return NULL;
 }
 
+static inline int lookup_module_symbol_name(unsigned long addr, char *symname)
+{
+        return -ERANGE;
+}
+
 static inline int module_get_kallsym(unsigned int symnum, unsigned long *value,
                                         char *type, char *name,
                                         char *module_name, int *exported)