4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yury Norov <yno...@caviumnetworks.com>

commit 8351760ff5b2042039554b4948ddabaac644a976 upstream.

syzbot is catching stalls at __bitmap_parselist()
(https://syzkaller.appspot.com/bug?id=ad7e0351fbc90535558514a71cd3edc11681997a).
The trigger is

  unsigned long v = 0;
  bitmap_parselist("7:,", &v, BITS_PER_LONG);

which results in hitting infinite loop at

    while (a <= b) {
            off = min(b - a + 1, used_size);
            bitmap_set(maskp, a, off);
            a += group_size;
    }

due to used_size == group_size == 0.

Link: http://lkml.kernel.org/r/20180404162647.15763-1-yno...@caviumnetworks.com
Fixes: 0a5ce0831d04382a ("lib/bitmap.c: make bitmap_parselist() thread-safe and 
much faster")
Signed-off-by: Yury Norov <yno...@caviumnetworks.com>
Reported-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp>
Reported-by: syzbot <syzbot+6887cbb011c8054e8...@syzkaller.appspotmail.com>
Cc: Noam Camus <noa...@mellanox.com>
Cc: Rasmus Villemoes <li...@rasmusvillemoes.dk>
Cc: Matthew Wilcox <mawil...@microsoft.com>
Cc: Mauro Carvalho Chehab <mche...@kernel.org>
Cc: <sta...@vger.kernel.org>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 lib/bitmap.c      |    2 +-
 lib/test_bitmap.c |    4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -607,7 +607,7 @@ static int __bitmap_parselist(const char
                /* if no digit is after '-', it's wrong*/
                if (at_start && in_range)
                        return -EINVAL;
-               if (!(a <= b) || !(used_size <= group_size))
+               if (!(a <= b) || group_size == 0 || !(used_size <= group_size))
                        return -EINVAL;
                if (b >= nmaskbits)
                        return -ERANGE;
--- a/lib/test_bitmap.c
+++ b/lib/test_bitmap.c
@@ -255,6 +255,10 @@ static const struct test_bitmap_parselis
        {-EINVAL, "-1", NULL, 8, 0},
        {-EINVAL, "-0", NULL, 8, 0},
        {-EINVAL, "10-1", NULL, 8, 0},
+       {-EINVAL, "0-31:", NULL, 8, 0},
+       {-EINVAL, "0-31:0", NULL, 8, 0},
+       {-EINVAL, "0-31:0/0", NULL, 8, 0},
+       {-EINVAL, "0-31:1/0", NULL, 8, 0},
        {-EINVAL, "0-31:10/1", NULL, 8, 0},
 };
 


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