[PATCH 4.15 30/53] lib: fix stall in __bitmap_parselist()

[Greg Kroah-Hartman]

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

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

From: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>

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-ynorov@xxxxxxxxxxxxxxxxxx
Fixes: 0a5ce0831d04382a ("lib/bitmap.c: make bitmap_parselist() thread-safe and much faster")
Signed-off-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Reported-by: syzbot <syzbot+6887cbb011c8054e8a3d@xxxxxxxxxxxxxxxxxxxxxxxxx>
Cc: Noam Camus <noamca@xxxxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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
@@ -218,6 +218,10 @@ 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},
 };