*** This bug is a security vulnerability ***
You have been subscribed to a public security bug by Seth Arnold (seth-arnold):
# Floating Point Exception
## Overview
As a result of invalid input validation (CWE-233: Improper Handling of
Parameters), specific files passed to the command line application,
`crasm`, can lead to a divide by zero fault (CWE-369: Divide By Zero) in
the function `opdiv`.
## About
`crasm` is a command line utility available on the Ubuntu package
manager and [GitHub][crasm-github] which assembles code for the 6800,
6801, 6803, 6502, 65C02, and Z80. At the time of writing, the current
version is 1.8-3 on Ubuntu and commit [5471a9f][5471a9f] on GitHub.
## Vulnerability
The parameter `presult` and it's members are not checked prior to a
division operation. As a result a floating point exception will occur
with `value` is zero and subsequently divided by itself.
```C
void opdiv(struct result* presult, struct result* parg)
{
presult->flags |= parg->flags;
checktype(presult, L_ABSOLUTE);
checktype(parg, L_ABSOLUTE);
presult->value /= parg->value;
}
```
### Affected versions
- 1.8-3 (as of writing, the current version) available on the Ubuntu package
manager.
- Versions compiled from commit `932f3293f96f36bfe32f8d8d70a5ba693d3b3193` and
below.
### Minimum Viable Patch
A patch was submitted to the maintainer and merged into the source
repository with [merge request #7][crasm-pr] containing the patch below.
The version installed with Ubuntu (22.10 and 22.04) remain vulnerable as
of writing.
```c
diff --git a/src/operator.c b/src/operator.c
index a28ac88..e589756 100644
--- a/src/operator.c
+++ b/src/operator.c
@@ -412,7 +412,10 @@ void opdiv(struct result* presult, struct result* parg)
presult->flags |= parg->flags;
checktype(presult, L_ABSOLUTE);
checktype(parg, L_ABSOLUTE);
- presult->value /= parg->value;
+ if (parg->value != 0)
+ {
+ presult->value /= parg->value;
+ }
}
void oprlist(struct result* presult, struct result* parg)
```
### Recommended Common Vulnerability Score
- Overall: 1.6
- CVSS Base Score: 1.7
- Impact Subscore: 1.4
- Exploitability Subscore: 0.3
## Validation:
To validate the existence of the floating point exception, use the
include test case to cause a fault. The file is passed in as the first
argument to the program.
```shell
$ lsb_release -rd
Description: Ubuntu 22.04.1 LTS
Release: 22.04
# Using apt
$ apt update
$ apt install crasm
$ apt list | grep crasm
crasm/jammy,now 1.8-3 amd64 [installed]
$ crasm /517d1b402d585fdb0458f96802a616419b9112bdc119a2393c35e034576a0c62
Pass #1
Floating point exception
# Using git
$ apt install git make clang
$ git clone https://github.com/colinbourassa/crasm.git
$ cd crasm
$ git checkout 932f3293f96f36bfe32f8d8d70a5ba693d3b3193
$ CC=clang make
8 warnings generated.
clang -O -Wall -c -o cpuz80.o cpuz80.c
clang -O -Wall -o crasm crasm.o stdvocabulary.o pseudos.o macro.o label.o
parse.o filter.o operator.o output.o xref.o scode.o cpulist.o cpu6800.o
cpu6502.o cpuz80.o -lm
done
make[1]: Leaving directory '/crasm/src'
./src/crasm /517d1b402d585fdb0458f96802a616419b9112bdc119a2393c35e034576a0c62
Pass #1
Floating point exception
```
### Backtrace
Observe the exception with `lldb`'s backtrace.
```text
$ lldb -- ./crasm
./517d1b402d585fdb0458f96802a616419b9112bdc119a2393c35e034576a0c62
(lldb) target create "./crasm"
Current executable set to '/crasm/src/crasm' (x86_64).
(lldb) settings set -- target.run-args
"./517d1b402d585fdb0458f96802a616419b9112bdc119a2393c35e034576a0c62"
(lldb) r
Process 2564 launched: '/crasm/src/crasm' (x86_64)
Pass #1
Process 2564 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_ARITHMETIC
(code=EXC_I386_DIV, subcode=0x0)
frame #0: 0x00000001000078f4 crasm`opdiv(presult=0x0000000100017468,
parg=0x00007ff7bfefefa0) at operator.c:415:18
412 presult->flags |= parg->flags;
413 checktype(presult, L_ABSOLUTE);
414 checktype(parg, L_ABSOLUTE);
-> 415 presult->value /= parg->value;
416 }
417
418 void oprlist(struct result* presult, struct result* parg)
Target 0: (crasm) stopped.
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_ARITHMETIC
(code=EXC_I386_DIV, subcode=0x0)
* frame #0: 0x00000001000078f4 crasm`opdiv(presult=0x0000000100017468,
parg=0x00007ff7bfefefa0) at operator.c:415:18
frame #1: 0x0000000100006455 crasm`parse2(expr="ed/maica",
presult=0x0000000100017468) at parse.c:152:7
frame #2: 0x00000001000062b4 crasm`parse(expr="ed/maica") at parse.c:233:3
frame #3: 0x0000000100009357 crasm`findmode(oper="aciam/de",
pvalue=0x00007ff7bfeff068) at cpu6800.c:99:11
frame #4: 0x0000000100009214 crasm`standard(code=202,
label=0x0000000000000000, mnemo="orab", oper="aciam/de") at cpu6800.c:163:9
frame #5: 0x0000000100002d3c crasm`asmline(s="orab aciam/de", status=3) at
crasm.c:562:7
frame #6: 0x0000000100002781 crasm`pass(n=1) at crasm.c:274:9
frame #7: 0x0000000100002460 crasm`crasm(flag=138) at crasm.c:180:3
frame #8: 0x0000000100002262 crasm`main(argc=0, argv=0x00007ff7bfeff440) at
crasm.c:147:5
frame #9: 0x00007ff812381310 dyld`start + 2432
```
[crasm-ubuntu]: https://packages.ubuntu.com/kinetic/crasm
[crasm-github]: https://github.com/colinbourassa/crasm
[5471a9f]:
https://github.com/colinbourassa/crasm/commit/5471a9f991fa795a1e86568cf5b4433e6c169047
** Affects: crasm (Ubuntu)
Importance: Undecided
Status: New
** Tags: jammy kinetic
--
Floating Point Exception in User Input
https://bugs.launchpad.net/bugs/2000021
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