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    <p>Create a large file such that reading <code>row</code> and <code>cols</code> are both negatives. <code>rasterBytes = pixBytes * rows * cols</code> is <em>positive</em> so everything will be fine till <code>p = img-&gt;raster;</code>. But at this point you have two infinite loops, and the program may overwrite the heap.</p> <p>Another attack is to set up <code>row</code> and <code>cols</code> such that they have different sign. You can choose either value to be <code>-1</code>, while the other is large enough to read the data you want. The allocation </p> <pre><code> img-&gt;raster = (void*)malloc(rasterBytes); </code></pre> <p>will fail, which lead img->raster to point to NULL. Which means</p> <pre><code> fread(p, pixBytes, 1, fp) &lt; 1 </code></pre> <p>will try to read the content of the file to kernel memory. If this code is executed in kernel mode, depending of the system (let say old unix which doesn use memory segment), then you will overwrite the content of the kernel memory with the content of the file. A kernel which doesn use memory segment rely not on segmentation faults but on page faults (a virtual address which doesnt have any real page assigned to it). The issue is that there are virtual memory designs such that the first real pages are directly assigned to the kernel pages. Ie kernel virtual address 0x0 is correspond to the real memory at 0x0 and is perfectly valid (inside the kernel).</p> <p><strong>EDIT:</strong> In both of those cases, the goal of the attacker is to inject the content of the input file (which is totally under his control) in a region of memory he should not have access to, while not being able to modify the function <code>read_ppm()</code>.</p>
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    1. COSo basically, depending on the platform and priviledges, the unchecked malloc can actually be exploited? I guess it's not something you can do nowadays, but it's likely the expected answer since the other malloc in the code is checked.
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    2. COyes but the attacker already did his job to write down the content of the file inside the heap
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    3. CO@Cesar I am not good in modern architecture, but we had an OS course which followed design purely based on pagination. Debugging inside the kernel was not easy, because you could just choose a number at random, start writing into it and everything runs fine.
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