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authorKees Cook2017-06-23 17:08:57 -0500
committerGreg Kroah-Hartman2017-06-29 05:48:50 -0500
commit1d3d0f8b7cf758136ed36b30620442d989601737 (patch)
tree0b812c7d3390e1622f7b356c5847731d7ca5f8a8 /fs
parent22da7ca81a3aad1af021c770b578acad86d63681 (diff)
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fs/exec.c: account for argv/envp pointers
commit 98da7d08850fb8bdeb395d6368ed15753304aa0c upstream. 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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/exec.c28
1 files changed, 24 insertions, 4 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 3a6de10d3891..02153068a694 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -206,8 +206,26 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
206 206
207 if (write) { 207 if (write) {
208 unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start; 208 unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
209 unsigned long ptr_size;
209 struct rlimit *rlim; 210 struct rlimit *rlim;
210 211
212 /*
213 * Since the stack will hold pointers to the strings, we
214 * must account for them as well.
215 *
216 * The size calculation is the entire vma while each arg page is
217 * built, so each time we get here it's calculating how far it
218 * is currently (rather than each call being just the newly
219 * added size from the arg page). As a result, we need to
220 * always add the entire size of the pointers, so that on the
221 * last call to get_arg_page() we'll actually have the entire
222 * correct size.
223 */
224 ptr_size = (bprm->argc + bprm->envc) * sizeof(void *);
225 if (ptr_size > ULONG_MAX - size)
226 goto fail;
227 size += ptr_size;
228
211 acct_arg_size(bprm, size / PAGE_SIZE); 229 acct_arg_size(bprm, size / PAGE_SIZE);
212 230
213 /* 231 /*
@@ -225,13 +243,15 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
225 * to work from. 243 * to work from.
226 */ 244 */
227 rlim = current->signal->rlim; 245 rlim = current->signal->rlim;
228 if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) { 246 if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4)
229 put_page(page); 247 goto fail;
230 return NULL;
231 }
232 } 248 }
233 249
234 return page; 250 return page;
251
252fail:
253 put_page(page);
254 return NULL;
235} 255}
236 256
237static void put_arg_page(struct page *page) 257static void put_arg_page(struct page *page)