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, 5 insertions, 6 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 3b4fe21c7e94..0c2052c79243 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -278,16 +278,15 @@ static int proc_pid_auxv(struct task_struct *task, char *buffer)
  */
 static int proc_pid_wchan(struct task_struct *task, char *buffer)
 {
-        const char *sym_name;
         unsigned long wchan;
-        char namebuf[KSYM_NAME_LEN+1];
+        char symname[KSYM_NAME_LEN+1];
 
         wchan = get_wchan(task);
 
-        sym_name = kallsyms_lookup(wchan, NULL, NULL, NULL, namebuf);
-        if (sym_name)
-                return sprintf(buffer, "%s", sym_name);
-        return sprintf(buffer, "%lu", wchan);
+        if (lookup_symbol_name(wchan, symname) < 0)
+                return sprintf(buffer, "%lu", wchan);
+        else
+                return sprintf(buffer, "%s", symname);
 }
 #endif /* CONFIG_KALLSYMS */