Date: Tue, 7 Sep 2010 19:35:49 -0700 (PDT) From: Roland McGrath <roland@...hat.com> To: Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org> CC: linux-kernel@...r.kernel.org, oss-security@...ts.openwall.com, Solar Designer <solar@...nwall.com>, Kees Cook <kees.cook@...onical.com>, Al Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, Oleg Nesterov <oleg@...hat.com>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Neil Horman <nhorman@...driver.com>, linux-fsdevel@...r.kernel.org, pageexec@...email.hu, "Brad Spengler <spender@...ecurity.net> Eugene Teo" <eugene@...hat.com> Subject: [PATCH 1/3] setup_arg_pages: diagnose excessive argument size The CONFIG_STACK_GROWSDOWN variant of setup_arg_pages() does not check the size of the argument/environment area on the stack. When it is unworkably large, shift_arg_pages() hits its BUG_ON. This is exploitable with a very large RLIMIT_STACK limit, to create a crash pretty easily. Check that the initial stack is not too large to make it possible to map in any executable. We're not checking that the actual executable (or intepreter, for binfmt_elf) will fit. So those mappings might clobber part of the initial stack mapping. But that is just userland lossage that userland made happen, not a kernel problem. Signed-off-by: Roland McGrath <roland@...hat.com> --- fs/exec.c | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 2d94552..1b63237 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -594,6 +594,11 @@ int setup_arg_pages(struct linux_binprm *bprm, #else stack_top = arch_align_stack(stack_top); stack_top = PAGE_ALIGN(stack_top); + + if (unlikely(stack_top < mmap_min_addr) || + unlikely(vma->vm_end - vma->vm_start >= stack_top - mmap_min_addr)) + return -ENOMEM; + stack_shift = vma->vm_end - stack_top; bprm->p -= stack_shift;
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