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Date: Wed, 14 Feb 2018 16:24:16 -0200
From: Geraldo Netto <>
Subject: fwrite() - possible division by zero

Dear Friends,

I was playing with musl and I think I may have found an issue on fwrite():

This is the original code:

size_t fwrite(const void *restrict src, size_t size, size_t nmemb,
FILE *restrict f)
    size_t k, l = size*nmemb;
    if (!size) nmemb = 0;
    k = __fwritex(src, l, f);
    return k==l ? nmemb : k/size;

It seems we need to check the variable size on return because if size is zero
We'll have a division by zero and a segmentation fault

I'm sending the attached patch that changes the return as follows:

return k==l ? nmemb : (size != 0) ? k/size : k;

I don't know if this is the correct approach, so, feel free to
change/let me know how to fix :)
Hope it helps

Kind Regards,

Geraldo Netto
Sapere Aude => Non dvcor, dvco

Download attachment "0001-fwrite-avoid-segmentation-fault-when-size-0.patch" of type "application/octet-stream" (774 bytes)

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