Console.WriteLine can crash with specially crafted strings #1951
Description
It looks like using Console.WriteLine since 8.3.x crashes xamarin with a native crash. The crash occurs in printf, and didn't happen in 8.2.x. It looks like Console.WriteLine now calls a form of printf under the hood. If I try to log a string containing % characters, all hell breaks loose and it starts poking the stack for extra arguments and printing garbage. If I send enough, I get a crash (probably because it ends up dereferencing an invalid pointer somewhere on the stack). The string I provide is actually a reduced version of a string we're actually trying to log in our app. It's an url-encoded list of parameters to a web service (reduced for business purpose, but the reduced string crashes every time on my end as well)
Steps to Reproduce
- Call the following code anywhere
Console.WriteLine("%20lo%20lo%20m%20m%20s%20s%20s%20s%20s%20s%20s");
Expected Behavior
Writes the exact string to the console
Actual Behavior
App crashes (this is the crash I obtain in armeabi-v7a), with other strings you can get random garbage.
07-09 19:05:52.918 2275 2275 F DEBUG : signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x20
07-09 19:05:52.918 2275 2275 F DEBUG : Cause: null pointer dereference
07-09 19:05:52.918 2275 2275 F DEBUG : r0 00000020 r1 00000020 r2 00000001 r3 00000000
07-09 19:05:52.918 2275 2275 F DEBUG : r4 f416166a r5 00000010 r6 00000014 r7 ffffffff
07-09 19:05:52.918 2275 2275 F DEBUG : r8 c877abbc r9 ffffffff sl c877b034 fp d459a7f4
07-09 19:05:52.918 2275 2275 F DEBUG : ip f415f594 sp c877ab18 lr f410c0fd pc f40e858c cpsr 600b0030
07-09 19:05:52.919 2275 2275 F DEBUG :
07-09 19:05:52.919 2275 2275 F DEBUG : backtrace:
07-09 19:05:52.919 2275 2275 F DEBUG : #00 pc 0001a58c /system/lib/libc.so (strlen+71)
07-09 19:05:52.919 2275 2275 F DEBUG : #1 pc 0003e0f9 /system/lib/libc.so (__vfprintf+3700)
07-09 19:05:52.919 2275 2275 F DEBUG : #2 pc 000454f5 /system/lib/libc.so (vasprintf+116)
07-09 19:05:52.919 2275 2275 F DEBUG : #3 pc 002bad20 /data/app/com.test.app-bNvAnqhOfjZ5uOWEHcDGDA==/lib/arm/libmonosgen-2.0.so (monoeg_g_log+80)
Version Information
Microsoft Visual Studio Professional 2017
Version 15.7.4
VisualStudio.15.Release/15.7.4+27703.2035
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