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The fragile stack expansion mechanism poses a security threat: if the The end address of the heap memory region - the heap always grows up). Heap memory, and the kernel expands the heap accordingly (it increases Process uses the brk() system-call to tell the kernel that it needs more In contrast, the heap expansion mechanism is explicit and robust: the the process cannot tell that its stack-pointer moved from the stack the kernel cannot tell that the process needed more stack memory The stack into the other memory region without raising a page-fault, Mapped directly below the stack, then the stack-pointer can move from It relies on page-fault exceptions, but if another memory region is Unfortunately, this stack expansion mechanism is implicit and fragile:
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or it terminates the process with a SIGSEGV if the stack expansionįails (for example, if the RLIMIT_STACK is reached). Of the process (it decreases the start address of the stack), and the page-fault handler transparently expands the user-space stack then a "page-fault" exception is raised and caught by the kernel, The stack and the unmapped memory pages below (the stack grows down, if the stack-pointer (the esp register, on i386) reaches the start of The user-space stack of a process is automatically expanded by the Of its memory region we do not use the ambiguous terms "top of the Of its memory region, and the "end of the stack" is the highest address
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Note: in this advisory, the "start of the stack" is the lowest address a proof-of-concept for CVE-2017-1085 in FreeBSD's setrlimit() NetBSD's stack guard-page implementation a proof-of-concept against /usr/bin/at on i386 OpenBSD, forĬVE-2017-1000372 in OpenBSD's stack guard-page implementation andĬVE-2017-1000373 in OpenBSD's qsort() function a local proof-of-concept that gains rip control against Exim a proof-of-concept that gains eip control against Sudo on i386 a local-root exploit against ld.so and most SUID-root PIEs a local-root exploit against ld.so and most SUID-root binaries an independent Sudoer-to-root exploit against CVE-2017-1000367 on any To illustrate our findings, we developed the following exploits and Stack with the other memory region, or the other memory region with "Smashing" the stack, or the other memory region: we overwrite the The stack and into the other memory region, without accessing the "Jumping" over the stack guard-page: we move the stack-pointer from Until the stack reaches another memory region, or until another memory "Clashing" the stack with another memory region: we allocate memory Multiple vulnerabilities in guard-page implementations, and devised User-space, and exploitable despite the stack guard-page we discovered In this advisory, we show that stack-clashes are widespread in Stack-clashes (a "guard-page" mapped below the stack): They were written before Linux introduced a protection against The only public exploits are Gael Delalleau's and Rafal Wojtczuk's, and In user-space, however, this problem has been greatly underestimated Since 2010, security researchers have exploited several stack-clashes Stack-clash exploit in user-space (CVE-2010-2240): Vulnerabilities in Xorg server running on Linux", the second In 2010, Rafal Wojtczuk published "Exploiting large memory management Vulnerabilities" and the first stack-clash exploit in user-space In 2005, Gael Delalleau presented "Large memory management Our research started with a 96-megabyte surprise:ī97bb000-b97dc000 rw-p 00000000 00:00 0 īf7c6000-bf806000 rw-p 00000000 00:00 0 Īnd a 12-year-old question: "If the heap grows up, and the stack growsĭown, what happens when they clash? Is it exploitable? How?" Qualys Security Advisory - The Stack Clash