Undefined behavior in img.c

[Matěj Plch]

Hi, therion uses img.h and img.c, and when I compile and run therion with Undefined Behavior Sanitizer, this error appears:

UndefinedBehaviorSanitizer: undefined-behavior
../extern/img.c:103:27: runtime error: left shift of 255 by 24 places cannot be represented in type 'int'

Problem is in function get32(), where shifting of signed value by 24 bits interferes with a sign bit. Bitwise operations should be done with unsigned types.

Therion CI job where this error occured: ​https://github.com/Afforix/therion/runs/2025117514?check_suite_focus=true.

[Olly Betts]

Thanks for reporting.

This also affects Survex itself, but only on big-endian platforms (on little-endian platforms it uses an optimised version of get32() which instead reads 4 bytes from the file in one go) so despite testing Survex with ubsan I hadn't spotted this.

[Olly Betts]

Fixed in 136cff23f5d5ca974c2ca2b68e8aaaadb2076307

[Olly Betts]

Oops, you actually need 227fd9a441d475ad9f79226a8da05a973e10dcd1 as I missed a change (sorry, the power tripped while I was preparing the commit and I lost track of where I'd got to when I turned my computer back on...)

[Matěj Plch]

Issue is fixed, thank you.