Make the taint flags reliable

It's somewhat unlikely that it happens, but right now a race window
between interrupts or machine checks or oopses could corrupt the tainted
bitmap because it is modified in a non atomic fashion.

Convert the taint variable to an unsigned long and use only atomic bit
operations on it.

Unfortunately this means the intvec sysctl functions cannot be used on it
anymore.

It turned out the taint sysctl handler could actually be simplified a bit
(since it only increases capabilities) so this patch actually removes
code.

[akpm@linux-foundation.org: remove unneeded include]
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 46 insertions, 17 deletions

diff --git a/kernel/panic.c b/kernel/panic.c
index 12c5a0a6c89b..028013f7afd4 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -23,7 +23,7 @@
 #include <linux/kallsyms.h>
 
 int panic_on_oops;
-int tainted;
+static unsigned long tainted_mask;
 static int pause_on_oops;
 static int pause_on_oops_flag;
 static DEFINE_SPINLOCK(pause_on_oops_lock);
@@ -159,31 +159,60 @@ EXPORT_SYMBOL(panic);
  *      The string is overwritten by the next call to print_taint().
  */
 
+struct tnt {
+        u8 bit;
+        char true;
+        char false;
+};
+
+static const struct tnt tnts[] = {
+        { TAINT_PROPRIETARY_MODULE, 'P', 'G' },
+        { TAINT_FORCED_MODULE, 'F', ' ' },
+        { TAINT_UNSAFE_SMP, 'S', ' ' },
+        { TAINT_FORCED_RMMOD, 'R', ' ' },
+        { TAINT_MACHINE_CHECK, 'M', ' ' },
+        { TAINT_BAD_PAGE, 'B', ' ' },
+        { TAINT_USER, 'U', ' ' },
+        { TAINT_DIE, 'D', ' ' },
+        { TAINT_OVERRIDDEN_ACPI_TABLE, 'A', ' ' },
+        { TAINT_WARN, 'W', ' ' },
+};
+
 const char *print_tainted(void)
 {
-        static char buf[20];
-        if (tainted) {
-                snprintf(buf, sizeof(buf), "Tainted: %c%c%c%c%c%c%c%c%c%c",
-                        tainted & TAINT_PROPRIETARY_MODULE ? 'P' : 'G',
-                        tainted & TAINT_FORCED_MODULE ? 'F' : ' ',
-                        tainted & TAINT_UNSAFE_SMP ? 'S' : ' ',
-                        tainted & TAINT_FORCED_RMMOD ? 'R' : ' ',
-                        tainted & TAINT_MACHINE_CHECK ? 'M' : ' ',
-                        tainted & TAINT_BAD_PAGE ? 'B' : ' ',
-                        tainted & TAINT_USER ? 'U' : ' ',
-                        tainted & TAINT_DIE ? 'D' : ' ',
-                        tainted & TAINT_OVERRIDDEN_ACPI_TABLE ? 'A' : ' ',
-                        tainted & TAINT_WARN ? 'W' : ' ');
-        }
-        else
+        static char buf[ARRAY_SIZE(tnts) + sizeof("Tainted: ") + 1];
+
+        if (tainted_mask) {
+                char *s;
+                int i;
+
+                s = buf + sprintf(buf, "Tainted: ");
+                for (i = 0; i < ARRAY_SIZE(tnts); i++) {
+                        const struct tnt *t = &tnts[i];
+                        *s++ = test_bit(t->bit, &tainted_mask) ?
+                                        t->true : t->false;
+                }
+                *s = 0;
+        } else
                 snprintf(buf, sizeof(buf), "Not tainted");
         return(buf);
 }
 
+int test_taint(unsigned flag)
+{
+        return test_bit(flag, &tainted_mask);
+}
+EXPORT_SYMBOL(test_taint);
+
+unsigned long get_taint(void)
+{
+        return tainted_mask;
+}
+
 void add_taint(unsigned flag)
 {
         debug_locks = 0; /* can't trust the integrity of the kernel anymore */
-        tainted |= flag;
+        set_bit(flag, &tainted_mask);
 }
 EXPORT_SYMBOL(add_taint);