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, 4 insertions, 6 deletions

diff --git a/kernel/time/timer_stats.c b/kernel/time/timer_stats.c
index 946ed45f7d2f..868f1bceb07f 100644
--- a/kernel/time/timer_stats.c
+++ b/kernel/time/timer_stats.c
@@ -257,14 +257,12 @@ void timer_stats_update_stats(void *timer, pid_t pid, void *startf,
 
 static void print_name_offset(struct seq_file *m, unsigned long addr)
 {
-        char namebuf[KSYM_NAME_LEN+1];
-        const char *sym_name;
+        char symname[KSYM_NAME_LEN+1];
 
-        sym_name = kallsyms_lookup(addr, NULL, NULL, NULL, namebuf);
-        if (sym_name)
-                seq_printf(m, "%s", sym_name);
-        else
+        if (lookup_symbol_name(addr, symname) < 0)
                 seq_printf(m, "<%p>", (void *)addr);
+        else
+                seq_printf(m, "%s", symname);
 }
 
 static int tstats_show(struct seq_file *m, void *v)