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SubjectRe: [PATCH c/r -mm] c/r: prctl: Simplify PR_SET_MM on mm::code/data assignment
Quoting Cyrill Gorcunov (gorcunov@openvz.org):
> On Tue, Apr 17, 2012 at 11:19:16PM +0400, Cyrill Gorcunov wrote:
> ...
> > > Since this is CAP_SYS_RESOURCE, and mmap_min_addr is CAP_SYS_RAWIO,
> > > how about a lower-bounds check against mmap_min_addr? (We're already
> > > doing the TASK_SIZE upper check, so this additional sanity checking
> > > seems reasonable to me.)
> >
> > I think this is good idea, thanks Kees. I'll check it out.
>
> Updated and tested version is below.
>
> Cyrill
> ---
> From: Cyrill Gorcunov <gorcunov@openvz.org>
> Subject: [PATCH] c/r: prctl: Simplify PR_SET_MM on mm::code/data assignment v2
>
> The mm::start_code, end_code, start_data, end_data members
> are set during startup of executable file and are not changed
> after.
>
> But the program itself might map new executable or/and data areas in
> time so the original values written into mm fields mentioned above
> might not have correspond VMA area at all, thus if one try to
> use this prctl codes without underlied VMA, the error will be
> returned.
>
> Drop this requirement. This shrinks the code and eliminates
> redundant calls to vma_flags_mismatch. The worst thing one can
> do (if say to write some bad values here) -- the weird results
> will be shown in /proc/$pid/statm or in /proc/pid/stat.
>
> Still, assignement of data on stack (such as command line and
> environment variables) requires the underlied VMA to exist.
>
> v2:
> Also make sure the address being set is greater than mmap_min_addr.
> Suggested by Kees Cook.

Thanks for that, Kees.

>
> Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Serge Hallyn <serge.hallyn@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> Cc: Pavel Emelyanov <xemul@parallels.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
> kernel/sys.c | 36 +++++++++---------------------------
> 1 file changed, 9 insertions(+), 27 deletions(-)
>
> Index: linux-2.6.git/kernel/sys.c
> ===================================================================
> --- linux-2.6.git.orig/kernel/sys.c
> +++ linux-2.6.git/kernel/sys.c
> @@ -1771,44 +1771,24 @@ static int prctl_set_mm(int opt, unsigne
> if (opt == PR_SET_MM_EXE_FILE)
> return prctl_set_mm_exe_file(mm, (unsigned int)addr);
>
> - if (addr >= TASK_SIZE)
> + if (addr >= TASK_SIZE || addr < mmap_min_addr)
> return -EINVAL;
>
> down_read(&mm->mmap_sem);
> vma = find_vma(mm, addr);
>
> - if (opt != PR_SET_MM_START_BRK &&
> - opt != PR_SET_MM_BRK &&
> - opt != PR_SET_MM_AUXV) {
> - /* It must be existing VMA */
> - if (!vma || vma->vm_start > addr)
> - goto out;
> - }
> -
> - error = -EINVAL;
> switch (opt) {
> case PR_SET_MM_START_CODE:
> + mm->start_code = addr;
> + break;
> case PR_SET_MM_END_CODE:
> - if (vma_flags_mismatch(vma, VM_READ | VM_EXEC,
> - VM_WRITE | VM_MAYSHARE))
> - goto out;
> -
> - if (opt == PR_SET_MM_START_CODE)
> - mm->start_code = addr;
> - else
> - mm->end_code = addr;
> + mm->end_code = addr;
> break;
> -
> case PR_SET_MM_START_DATA:
> + mm->start_data = addr;
> + break;
> case PR_SET_MM_END_DATA:
> - if (vma_flags_mismatch(vma, VM_READ | VM_WRITE,
> - VM_EXEC | VM_MAYSHARE))
> - goto out;
> -
> - if (opt == PR_SET_MM_START_DATA)
> - mm->start_data = addr;
> - else
> - mm->end_data = addr;
> + mm->end_data = addr;
> break;
>
> case PR_SET_MM_START_BRK:
> @@ -1847,6 +1827,8 @@ static int prctl_set_mm(int opt, unsigne
> case PR_SET_MM_ARG_END:
> case PR_SET_MM_ENV_START:
> case PR_SET_MM_ENV_END:
> + if (!vma)
> + goto out;
> #ifdef CONFIG_STACK_GROWSUP
> if (vma_flags_mismatch(vma, VM_READ | VM_WRITE | VM_GROWSUP, 0))
> #else


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