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[PATCH 4.9 06/44] fs/exec.c: account for argv/envp pointers

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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@chromium.org>

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>

---
 fs/exec.c |   28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -215,8 +215,26 @@ static struct page *get_arg_page(struct
 
 	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);
 
 		/*
@@ -234,13 +252,15 @@ static struct page *get_arg_page(struct
 		 *    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)

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[PATCH 4.9 00/44] 4.9.35-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:20 +0200
  [PATCH 4.9 16/44] HID: Add quirk for Dell PIXART OEM mouse Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:20 +0200
  [PATCH 4.9 14/44] CIFS: Improve readdir verbosity Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:20 +0200
  [PATCH 4.9 42/44] net: phy: fix marvell phy status reading Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:20 +0200
  [PATCH 4.9 10/44] perf/x86/intel: Add 1G DTLB load/store miss support for SKL Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:20 +0200
  [PATCH 4.9 07/44] powerpc/perf: Fix oops when kthread execs user process Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:20 +0200
  [PATCH 4.9 11/44] KVM: s390: gaccess: fix real-space designation asce handling for gmap shadows Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:20 +0200
  [PATCH 4.9 21/44] brcmfmac: add parameter to pass error code in firmware callback Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:20 +0200
  [PATCH 4.9 37/44] usb: gadget: f_fs: avoid out of bounds access on comp_desc Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:20 +0200
  [PATCH 4.9 15/44] cxgb4: notify uP to route ctrlq compl to rdma rspq Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:20 +0200
  [PATCH 4.9 35/44] of: Add check to of_scan_flat_dt() before accessing initial_boot_params Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 06/44] fs/exec.c: account for argv/envp pointers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 27/44] target: Fix kref->refcount underflow in transport_cmd_finish_abort Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 12/44] KVM: PPC: Book3S HV: Preserve userspace HTM state properly Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 03/44] xen-blkback: dont leak stack data via response ring Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 09/44] lib/cmdline.c: fix get_options() overflow while parsing ranges Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 23/44] brcmfmac: unbind all devices upon failure in firmware callback Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 38/44] rt2x00: avoid introducing a USB dependency in the rt2x00lib module Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 28/44] iscsi-target: Fix delayed logout processing greater than SECONDS_FOR_LOGOUT_COMP Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 05/44] ALSA: pcm: Dont treat NULL chmap as a fatal error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 30/44] drm/radeon: add a PX quirk for another K53TK variant Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 26/44] arm64/vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 22/44] brcmfmac: use firmware callback upon failure to load Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 04/44] ALSA: firewire-lib: Fix stall of process context at packet error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 08/44] autofs: sanity check status reported with AUTOFS_DEV_IOCTL_FAIL Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 40/44] dmaengine: bcm2835: Fix cyclic DMA period splitting Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 31/44] drm/radeon: add a quirk for Toshiba Satellite L20-183 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 19/44] powerpc/64s: Handle data breakpoints in Radix mode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 39/44] net: phy: Initialize mdio clock at probe function Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 25/44] time: Fix CLOCK_MONOTONIC_RAW sub-nanosecond accounting Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 29/44] iscsi-target: Reject immediate data underflow larger than SCSI transfer length Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:40 +0200
  [PATCH 4.9 20/44] Input: i8042 - add Fujitsu Lifebook AH544 to notimeout list Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:50 +0200
  [PATCH 4.9 18/44] powerpc/kprobes: Pause function_graph tracing during jprobes handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 16:50 +0200
  Re: [PATCH 4.9 00/44] 4.9.35-stable review Sumit Semwal <sumit.semwal@linaro.org> - 2017-06-27 19:40 +0200
    Re: [PATCH 4.9 00/44] 4.9.35-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-28 14:10 +0200
  Re: [PATCH 4.9 00/44] 4.9.35-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-27 20:40 +0200
  Re: [PATCH 4.9 00/44] 4.9.35-stable review Guenter Roeck <linux@roeck-us.net> - 2017-06-27 21:10 +0200
  Re: [PATCH 4.9 00/44] 4.9.35-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-06-28 16:00 +0200

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