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4c390211 TL |
1 | From 6b44f156198491839655077fc7f3a469c67e1f8d Mon Sep 17 00:00:00 2001 |
2 | From: Kees Cook <keescook@chromium.org> | |
3 | Date: Wed, 12 Jul 2017 15:30:39 +0200 | |
4 | Subject: [PATCH 2/3] fs/exec.c: account for argv/envp pointers | |
5 | ||
6 | When limiting the argv/envp strings during exec to 1/4 of the stack limit, | |
7 | the storage of the pointers to the strings was not included. This means | |
8 | that an exec with huge numbers of tiny strings could eat 1/4 of the stack | |
9 | limit in strings and then additional space would be later used by the | |
10 | pointers to the strings. | |
11 | ||
12 | For example, on 32-bit with a 8MB stack rlimit, an exec with 1677721 | |
13 | single-byte strings would consume less than 2MB of stack, the max (8MB / | |
14 | 4) amount allowed, but the pointers to the strings would consume the | |
15 | remaining additional stack space (1677721 * 4 == 6710884). | |
16 | ||
17 | The result (1677721 + 6710884 == 8388605) would exhaust stack space | |
18 | entirely. Controlling this stack exhaustion could result in | |
19 | pathological behavior in setuid binaries (CVE-2017-1000365). | |
20 | ||
21 | [akpm@linux-foundation.org: additional commenting from Kees] | |
22 | Fixes: b6a2fea39318 ("mm: variable length argument support") | |
23 | Link: http://lkml.kernel.org/r/20170622001720.GA32173@beast | |
24 | Signed-off-by: Kees Cook <keescook@chromium.org> | |
25 | Acked-by: Rik van Riel <riel@redhat.com> | |
26 | Acked-by: Michal Hocko <mhocko@suse.com> | |
27 | Cc: Alexander Viro <viro@zeniv.linux.org.uk> | |
28 | Cc: Qualys Security Advisory <qsa@qualys.com> | |
29 | Cc: <stable@vger.kernel.org> | |
30 | Signed-off-by: Andrew Morton <akpm@linux-foundation.org> | |
31 | Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> | |
32 | ||
33 | CVE-2017-1000365 | |
34 | ||
35 | (cherry-picked from commit 98da7d08850fb8bdeb395d6368ed15753304aa0c) | |
36 | Signed-off-by: Stefan Bader <stefan.bader@canonical.com> | |
37 | Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> | |
38 | Acked-by: Seth Forshee <seth.forshee@canonical.com> | |
39 | Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> | |
40 | ||
41 | Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com> | |
42 | --- | |
43 | fs/exec.c | 28 ++++++++++++++++++++++++---- | |
44 | 1 file changed, 24 insertions(+), 4 deletions(-) | |
45 | ||
46 | diff --git a/fs/exec.c b/fs/exec.c | |
47 | index 9fb90c37c37f..8cf76e2a0b83 100644 | |
48 | --- a/fs/exec.c | |
49 | +++ b/fs/exec.c | |
50 | @@ -225,8 +225,26 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, | |
51 | ||
52 | if (write) { | |
53 | unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start; | |
54 | + unsigned long ptr_size; | |
55 | struct rlimit *rlim; | |
56 | ||
57 | + /* | |
58 | + * Since the stack will hold pointers to the strings, we | |
59 | + * must account for them as well. | |
60 | + * | |
61 | + * The size calculation is the entire vma while each arg page is | |
62 | + * built, so each time we get here it's calculating how far it | |
63 | + * is currently (rather than each call being just the newly | |
64 | + * added size from the arg page). As a result, we need to | |
65 | + * always add the entire size of the pointers, so that on the | |
66 | + * last call to get_arg_page() we'll actually have the entire | |
67 | + * correct size. | |
68 | + */ | |
69 | + ptr_size = (bprm->argc + bprm->envc) * sizeof(void *); | |
70 | + if (ptr_size > ULONG_MAX - size) | |
71 | + goto fail; | |
72 | + size += ptr_size; | |
73 | + | |
74 | acct_arg_size(bprm, size / PAGE_SIZE); | |
75 | ||
76 | /* | |
77 | @@ -244,13 +262,15 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, | |
78 | * to work from. | |
79 | */ | |
80 | rlim = current->signal->rlim; | |
81 | - if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) { | |
82 | - put_page(page); | |
83 | - return NULL; | |
84 | - } | |
85 | + if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) | |
86 | + goto fail; | |
87 | } | |
88 | ||
89 | return page; | |
90 | + | |
91 | +fail: | |
92 | + put_page(page); | |
93 | + return NULL; | |
94 | } | |
95 | ||
96 | static void put_arg_page(struct page *page) | |
97 | -- | |
98 | 2.11.0 | |
99 |