Check tokens[0] after allocating memory

[imzhuhl]

Bug report

I have questions when reading the source code of file pegen.c.
There is a code snippet in function _PyPegen_Parser_New:

p->tokens[0] = PyMem_Calloc(1, sizeof(Token));
if (!p->tokens) {
    PyMem_Free(p->tokens);
    PyMem_Free(p);
    return (Parser *) PyErr_NoMemory();
}

I think it makes more sense to check p->tokens[0] but not p->tokens in if condition.

I look at the PR #19669 where the code was introduced and no one discussed this. Is this an oversight, or am I wrong?

Your environment

• CPython versions tested on: main branch

[arhadthedev]

@AlexWaygood It seems to be a type-crash since PyMem_Calloc() failure is ignored leading to a C null pointer access somewhere below.

[AlexWaygood]

@AlexWaygood It seems to be a type-crash since PyMem_Calloc() failure is ignored leading to a C null pointer access somewhere below.

Sounds plausible, but I'm not much of a C programmer, so I'll let somebody else do the relabelling :)

[kumaraditya303]

Sounds plausible, but I'm not much of a C programmer, so I'll let somebody else do the relabelling :)

Ok done, it can indeed segfault if allocation fails, classic null dereference :)

[kumaraditya303]

Fixed by #95356, thanks for the report!