[PATCH v2] lib/string_helpers.c: fix infinite loop in string_get_size()

[Vitaly Kuznetsov]

Some string_get_size() calls (e.g.:
 string_get_size(1, 512, STRING_UNITS_10, ..., ...)
 string_get_size(15, 64, STRING_UNITS_10, ..., ...)
) result in an infinite loop. The problem is that if size is equal to
divisor[units]/blk_size and is smaller than divisor[units] we'll end
up with size == 0 when we start doing sf_cap calculations:

For string_get_size(1, 512, STRING_UNITS_10, ..., ...) case:
   ...
   remainder = do_div(size, divisor[units]); -> size is 0, remainder is 1
   remainder *= blk_size; -> remainder is 512
   ...
   size *= blk_size; -> size is still 0
   size += remainder / divisor[units]; -> size is still 0

The caller causing the issue is sd_read_capacity(), the problem was noticed
on Hyper-V, such weird size was reported by host when scanning collides
with device removal. This is probably a separate issue worth fixing, this
patch is intended to prevent the library routing from infinite looping.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 lib/string_helpers.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index c98ae81..d0e607c 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -59,7 +59,7 @@ void string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
 	}
 
 	exp = divisor[units] / (u32)blk_size;
-	if (size >= exp) {
+	if (size > exp) {
 		remainder = do_div(size, divisor[units]);
 		remainder *= blk_size;
 		i++;
-- 
2.4.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/