__bitmap_parselist: fix bug in empty string handling

bitmap_parselist("", &mask, nmaskbits) will erroneously set bit zero in
the mask.  The same bug is visible in cpumask_parselist() since it is
layered on top of the bitmask code, e.g.  if you boot with "isolcpus=",
you will actually end up with cpu zero isolated.

The bug was introduced in commit 4b060420a596 ("bitmap, irq: add
smp_affinity_list interface to /proc/irq") when bitmap_parselist() was
generalized to support userspace as well as kernelspace.

Fixes: 4b060420a596 ("bitmap, irq: add smp_affinity_list interface to /proc/irq")
Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 64c0926..40162f8 100644 (file)
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -506,12 +506,12 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen,
        unsigned a, b;
        int c, old_c, totaldigits;
        const char __user __force *ubuf = (const char __user __force *)buf;
-       int exp_digit, in_range;
+       int at_start, in_range;
 
        totaldigits = c = 0;
        bitmap_zero(maskp, nmaskbits);
        do {
-               exp_digit = 1;
+               at_start = 1;
                in_range = 0;
                a = b = 0;
 
@@ -540,11 +540,10 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen,
                                break;
 
                        if (c == '-') {
-                               if (exp_digit || in_range)
+                               if (at_start || in_range)
                                        return -EINVAL;
                                b = 0;
                                in_range = 1;
-                               exp_digit = 1;
                                continue;
                        }
 
@@ -554,16 +553,18 @@ static int __bitmap_parselist(const char *buf, unsigned int buflen,
                        b = b * 10 + (c - '0');
                        if (!in_range)
                                a = b;
-                       exp_digit = 0;
+                       at_start = 0;
                        totaldigits++;
                }
                if (!(a <= b))
                        return -EINVAL;
                if (b >= nmaskbits)
                        return -ERANGE;
-               while (a <= b) {
-                       set_bit(a, maskp);
-                       a++;
+               if (!at_start) {
+                       while (a <= b) {
+                               set_bit(a, maskp);
+                               a++;
+                       }
                }
        } while (buflen && c == ',');
        return 0;