musl - musl - an implementation of the standard library for Linux-based systems

fix undefined behavior in scanf core

as reported/analyzed by Pascal Cuoq, the shlim and shcnt macros/functions are called by the scanf core (vfscanf) with f->rpos potentially null (if the FILE is not yet activated for reading at the time of the call). in this case, they compute differences between a null pointer (f->rpos) and a non-null one (f->buf), resulting in undefined behavior. it's unlikely that any observably wrong behavior occurred in practice, at least without LTO, due to limits on what's visible to the compiler from translation unit boundaries, but this has not been checked. fix is simply ensuring that the FILE is activated for read mode before entering the main scanf loop, and erroring out early if it can't be.

Diffstat (limited to 'src/stdio')

1 files changed, 3 insertions, 0 deletions