Bug 12926

Summary:	embedded "wc" command has overflow issues
Product:	Busybox	Reporter:	Benjamin Brecht <benjamin.bauer>
Component:	Other	Assignee:	unassigned
Status:	RESOLVED FIXED
Severity:	normal	CC:	busybox-cvs
Priority:	P5
Version:	unspecified
Target Milestone:	---
Hardware:	PC
OS:	Linux
Host:		Target:
Build:

Description Benjamin Brecht 2020-05-20 11:47:38 UTC

We use BusyBox within Alpine Linux 3.10 in a docker container.
Today we found out, that the "wc" utility is counting wrong above a certain size.
It looks to me like a overflow issue.


Example on Ubuntu Linux (ok):
# 1000 Byte (ok)
cat /dev/zero | pv --stop-at-size -s 1000 | wc -c
>> 1000

# 4 Gib (ok)
cat /dev/zero | pv --stop-at-size -s 4294967296 | wc -c
>> 4294967296


Example on Busybox (overflow at ~4 Gib):

#  4 Gib minus 1 Byte (ok)
cat /dev/zero | pv --stop-at-size -s 4294967295 | wc -c
>> 4294967295

# 4 Gib (overflow)
cat /dev/zero | pv --stop-at-size -s 4294967296 | wc -c
>> 0

Comment 1 Benjamin Brecht 2020-05-25 06:28:34 UTC

Code from: coreutils/wc.c

#if ENABLE_FEATURE_WC_LARGE
# define COUNT_T unsigned long long
# define COUNT_FMT "llu"
#else
# define COUNT_T unsigned
# define COUNT_FMT "u"
#endif

Can you enable this flag, so that the bigger variable type is used for counting?

Comment 2 Ron Yorston 2020-05-25 07:11:34 UTC

FEATURE_WC_LARGE is enabled by default. It looks as though the Alpine Linux developers have turned it off in their build. If you want it enabled there you'd have to ask them.

Comment 3 Benjamin Brecht 2020-05-25 07:28:16 UTC

Thanks for the pointer.

The bug was fixed in https://gitlab.alpinelinux.org/alpine/aports

alpine/aports$ git annotate main/busybox/busyboxconfig | grep WC_LARGE
bcf80db9586	(Sören Tempel	2020-03-13 12:51:36 +0100	336)CONFIG_FEATURE_WC_LARGE=y

git show bcf80db9586
...
@@ -333,7 +333,7 @@ CONFIG_UUDECODE=y
 CONFIG_BASE64=y
 CONFIG_UUENCODE=y
 CONFIG_WC=y
-# CONFIG_FEATURE_WC_LARGE is not set
+CONFIG_FEATURE_WC_LARGE=y

I will try a newer version of alpine.

Comment 4 Benjamin Brecht 2020-05-25 07:49:36 UTC

Bug is fixed in alpine >= 3.11.6.