| Message ID | 1499866239-22805-1-git-send-email-stefan.bader@canonical.com |
|---|---|
| State | New |
| Headers | show |
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
On 12.07.2017 15:30, Stefan Bader wrote: > From: Kees Cook <keescook@chromium.org> > > When limiting the argv/envp strings during exec to 1/4 of the stack limit, > the storage of the pointers to the strings was not included. This means > that an exec with huge numbers of tiny strings could eat 1/4 of the stack > limit in strings and then additional space would be later used by the > pointers to the strings. > > For example, on 32-bit with a 8MB stack rlimit, an exec with 1677721 > single-byte strings would consume less than 2MB of stack, the max (8MB / > 4) amount allowed, but the pointers to the strings would consume the > remaining additional stack space (1677721 * 4 == 6710884). > > The result (1677721 + 6710884 == 8388605) would exhaust stack space > entirely. Controlling this stack exhaustion could result in > pathological behavior in setuid binaries (CVE-2017-1000365). > > [akpm@linux-foundation.org: additional commenting from Kees] > Fixes: b6a2fea39318 ("mm: variable length argument support") > Link: http://lkml.kernel.org/r/20170622001720.GA32173@beast > Signed-off-by: Kees Cook <keescook@chromium.org> > Acked-by: Rik van Riel <riel@redhat.com> > Acked-by: Michal Hocko <mhocko@suse.com> > Cc: Alexander Viro <viro@zeniv.linux.org.uk> > Cc: Qualys Security Advisory <qsa@qualys.com> > Cc: <stable@vger.kernel.org> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> > > CVE-2017-1000365 > > (cherry-picked from commit 98da7d08850fb8bdeb395d6368ed15753304aa0c) > Signed-off-by: Stefan Bader <stefan.bader@canonical.com> > --- > > Fix already applied to Xenial via upstream stable updates. Can be > cherry-picked into Z/Y/T. > > -Stefan > > fs/exec.c | 28 ++++++++++++++++++++++++---- > 1 file changed, 24 insertions(+), 4 deletions(-) > > diff --git a/fs/exec.c b/fs/exec.c > index 72934df..9041990 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -220,8 +220,26 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, > > if (write) { > unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start; > + unsigned long ptr_size; > struct rlimit *rlim; > > + /* > + * Since the stack will hold pointers to the strings, we > + * must account for them as well. > + * > + * The size calculation is the entire vma while each arg page is > + * built, so each time we get here it's calculating how far it > + * is currently (rather than each call being just the newly > + * added size from the arg page). As a result, we need to > + * always add the entire size of the pointers, so that on the > + * last call to get_arg_page() we'll actually have the entire > + * correct size. > + */ > + ptr_size = (bprm->argc + bprm->envc) * sizeof(void *); > + if (ptr_size > ULONG_MAX - size) > + goto fail; > + size += ptr_size; > + > acct_arg_size(bprm, size / PAGE_SIZE); > > /* > @@ -239,13 +257,15 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, > * to work from. > */ > rlim = current->signal->rlim; > - if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) { > - put_page(page); > - return NULL; > - } > + if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) ^ Should have compiled first. We need to keep this as ACCESS_ONCE in Trusty. Will send a v2 for Trusty. -Stefan > + goto fail; > } > > return page; > + > +fail: > + put_page(page); > + return NULL; > } > > static void put_arg_page(struct page *page) >
On Wed, Jul 12, 2017 at 03:30:39PM +0200, Stefan Bader wrote: > From: Kees Cook <keescook@chromium.org> > > When limiting the argv/envp strings during exec to 1/4 of the stack limit, > the storage of the pointers to the strings was not included. This means > that an exec with huge numbers of tiny strings could eat 1/4 of the stack > limit in strings and then additional space would be later used by the > pointers to the strings. > > For example, on 32-bit with a 8MB stack rlimit, an exec with 1677721 > single-byte strings would consume less than 2MB of stack, the max (8MB / > 4) amount allowed, but the pointers to the strings would consume the > remaining additional stack space (1677721 * 4 == 6710884). > > The result (1677721 + 6710884 == 8388605) would exhaust stack space > entirely. Controlling this stack exhaustion could result in > pathological behavior in setuid binaries (CVE-2017-1000365). > > [akpm@linux-foundation.org: additional commenting from Kees] > Fixes: b6a2fea39318 ("mm: variable length argument support") > Link: http://lkml.kernel.org/r/20170622001720.GA32173@beast > Signed-off-by: Kees Cook <keescook@chromium.org> > Acked-by: Rik van Riel <riel@redhat.com> > Acked-by: Michal Hocko <mhocko@suse.com> > Cc: Alexander Viro <viro@zeniv.linux.org.uk> > Cc: Qualys Security Advisory <qsa@qualys.com> > Cc: <stable@vger.kernel.org> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> > > CVE-2017-1000365 > > (cherry-picked from commit 98da7d08850fb8bdeb395d6368ed15753304aa0c) > Signed-off-by: Stefan Bader <stefan.bader@canonical.com> For Y/Z: Acked-by: Seth Forshee <seth.forshee@canonical.com> Artful already got this commit from upstream stable.
Applied to yakkety and zesty master-next branches. Thanks. Cascardo.
diff --git a/fs/exec.c b/fs/exec.c index 72934df..9041990 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -220,8 +220,26 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, if (write) { unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start; + unsigned long ptr_size; struct rlimit *rlim; + /* + * Since the stack will hold pointers to the strings, we + * must account for them as well. + * + * The size calculation is the entire vma while each arg page is + * built, so each time we get here it's calculating how far it + * is currently (rather than each call being just the newly + * added size from the arg page). As a result, we need to + * always add the entire size of the pointers, so that on the + * last call to get_arg_page() we'll actually have the entire + * correct size. + */ + ptr_size = (bprm->argc + bprm->envc) * sizeof(void *); + if (ptr_size > ULONG_MAX - size) + goto fail; + size += ptr_size; + acct_arg_size(bprm, size / PAGE_SIZE); /* @@ -239,13 +257,15 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, * to work from. */ rlim = current->signal->rlim; - if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) { - put_page(page); - return NULL; - } + if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) + goto fail; } return page; + +fail: + put_page(page); + return NULL; } static void put_arg_page(struct page *page)