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92 lines
3.2 KiB
Diff
92 lines
3.2 KiB
Diff
From 2dff2164d171e9c27f2f7fa778d408ecf4d1e1ea Mon Sep 17 00:00:00 2001
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From: Kees Cook <keescook@chromium.org>
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Date: Fri, 23 Jun 2017 15:08:57 -0700
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Subject: fs/exec.c: account for argv/envp pointers
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commit 98da7d08850fb8bdeb395d6368ed15753304aa0c upstream.
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When limiting the argv/envp strings during exec to 1/4 of the stack limit,
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the storage of the pointers to the strings was not included. This means
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that an exec with huge numbers of tiny strings could eat 1/4 of the stack
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limit in strings and then additional space would be later used by the
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pointers to the strings.
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For example, on 32-bit with a 8MB stack rlimit, an exec with 1677721
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single-byte strings would consume less than 2MB of stack, the max (8MB /
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4) amount allowed, but the pointers to the strings would consume the
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remaining additional stack space (1677721 * 4 == 6710884).
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The result (1677721 + 6710884 == 8388605) would exhaust stack space
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entirely. Controlling this stack exhaustion could result in
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pathological behavior in setuid binaries (CVE-2017-1000365).
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[akpm@linux-foundation.org: additional commenting from Kees]
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Fixes: b6a2fea39318 ("mm: variable length argument support")
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Link: http://lkml.kernel.org/r/20170622001720.GA32173@beast
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Signed-off-by: Kees Cook <keescook@chromium.org>
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Acked-by: Rik van Riel <riel@redhat.com>
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Acked-by: Michal Hocko <mhocko@suse.com>
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Cc: Alexander Viro <viro@zeniv.linux.org.uk>
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Cc: Qualys Security Advisory <qsa@qualys.com>
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Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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fs/exec.c | 28 ++++++++++++++++++++++++----
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1 file changed, 24 insertions(+), 4 deletions(-)
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diff --git a/fs/exec.c b/fs/exec.c
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index fe9ec45..6fa04b3 100644
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--- a/fs/exec.c
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+++ b/fs/exec.c
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@@ -199,8 +199,26 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
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if (write) {
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unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
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+ unsigned long ptr_size;
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struct rlimit *rlim;
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+ /*
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+ * Since the stack will hold pointers to the strings, we
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+ * must account for them as well.
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+ *
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+ * The size calculation is the entire vma while each arg page is
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+ * built, so each time we get here it's calculating how far it
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+ * is currently (rather than each call being just the newly
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+ * added size from the arg page). As a result, we need to
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+ * always add the entire size of the pointers, so that on the
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+ * last call to get_arg_page() we'll actually have the entire
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+ * correct size.
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+ */
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+ ptr_size = (bprm->argc + bprm->envc) * sizeof(void *);
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+ if (ptr_size > ULONG_MAX - size)
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+ goto fail;
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+ size += ptr_size;
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+
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acct_arg_size(bprm, size / PAGE_SIZE);
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/*
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@@ -218,13 +236,15 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
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* to work from.
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*/
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rlim = current->signal->rlim;
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- if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) {
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- put_page(page);
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- return NULL;
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- }
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+ if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4)
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+ goto fail;
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}
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return page;
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+
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+fail:
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+ put_page(page);
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+ return NULL;
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}
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static void put_arg_page(struct page *page)
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--
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cgit v1.1
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