As mentioned previously, we need to know the distance of the freed chunk and the target region to unmap the target while also taking care of page alignment. This enables free to find the beginning of the mapped region when called on the chunk see below while retaining support for platforms that cannot partially unmap regions just a guess and avoiding costly munmap calls. I believe the binary itself is a less interesting target, similarly to the brk heap case above. Comments of any nature are welcome, hit me up on freenode or twitter. Since munmap supports partial unmappings, we can also hit a single page of a mapping if needed.

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Do not select a different address than the one specified.

A file descriptor refers to a non-regular file. All pages starting with addr and continuing for a length of len bytes are removed.

The effect of changing the size of the underlying file of a mapping. If gdb can invoke munmap using the ptrace interface, then you can write a program to do it – debuggers aren’t specially privileged. This post explores the possibilities arising from forcing free to unmap arbitrary regions of the address space and is part of the ptmalloc fanzine.


These would most realistically come from two leaks, the absolute address of the chunk and the absolute address of the target. The mapping is not backed by any file; its contents are.

munmap()–Remove Memory Mapping

It causes free to unmap the page containing the current stack frames, eventually leading to the ret instruction of munmap accessing the unmapped page, the kernel expanding the stack and the function returning to 0: Do not reserve swap space for this mapping. Also, the old PIE layout complicates things further. When swap space is reserved, one has the guarantee that it is possible to modify the mapping.

The contents of a file mapping are initialized using length bytes starting.

munmap(2) – Linux man page

The same holds for the opposite scenario: No, there is no way to unmap memory in one go. Pages may be read.

If a process calls mmap I’m thinking of a call something like munmap pid, You can see the maximum number of mappings per process with: Everything below is based on this primitive, even though some examples, for brevity, use munmap liux instead of emulating the corruption and subsequent free.

Indicates to the kernel virtual lijux. Abbreviated source code and output: In kernels before 2. This flag is ignored in older kernels.

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munmap.3p – Linux manual page

Sign up using Facebook. If the binary image itself is position independent, two things can happen: In what munma; munmap failed! Now imagine two or more large chunks mmapped consecutively, with at least one controlled by us.

It probably won’t be trivial though, as you’ll need to reimplement much of GDB’s code This error may also indicate that the value for the addr parameter is not a multiple of the page size. Indicates to the kernel VM system that munmal mapping should extend downwards in memory. The prot argument describes the desired memory protection of the. Why would I want to do that?

munmap()–Remove Memory Mapping

Sign up or log in Sign up using Google. From Linux Man page. Later accesses to the mapping will not be bocked by page faults.