From f32a03523e6877e63d5bf881ce54fe4e7daac0c7 Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Sun, 26 Feb 2017 20:51:00 +0000 Subject: [PATCH] ipc/shm: Fix shmat mmap nil-page protection (CVE-2017-5669) --- debian/changelog | 1 + ...m-fix-shmat-mmap-nil-page-protection.patch | 70 +++++++++++++++++++ debian/patches/series | 1 + 3 files changed, 72 insertions(+) create mode 100644 debian/patches/bugfix/all/ipc-shm-fix-shmat-mmap-nil-page-protection.patch diff --git a/debian/changelog b/debian/changelog index 6e738f123..e2f47f8b0 100644 --- a/debian/changelog +++ b/debian/changelog @@ -92,6 +92,7 @@ linux (4.9.13-1) UNRELEASED; urgency=medium * udeb: Add more USB host and dual-role drivers to usb-modules (Closes: #856111) * [x86] kvm: fix page struct leak in handle_vmon (CVE-2017-2596) + * ipc/shm: Fix shmat mmap nil-page protection (CVE-2017-5669) -- Ben Hutchings Sat, 18 Feb 2017 00:38:10 +0000 diff --git a/debian/patches/bugfix/all/ipc-shm-fix-shmat-mmap-nil-page-protection.patch b/debian/patches/bugfix/all/ipc-shm-fix-shmat-mmap-nil-page-protection.patch new file mode 100644 index 000000000..bed67eee4 --- /dev/null +++ b/debian/patches/bugfix/all/ipc-shm-fix-shmat-mmap-nil-page-protection.patch @@ -0,0 +1,70 @@ +From: Davidlohr Bueso +Date: Thu, 23 Feb 2017 11:41:32 +1100 +Subject: ipc/shm: Fix shmat mmap nil-page protection +Origin: https://marc.info/?l=linux-mm&m=148605021927245&w=2 +Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2017-5669 + +The issue is described here, with a nice testcase: + + https://bugzilla.kernel.org/show_bug.cgi?id=192931 + +The problem is that shmat() calls do_mmap_pgoff() with MAP_FIXED, and the +address rounded down to 0. For the regular mmap case, the protection +mentioned above is that the kernel gets to generate the address -- +arch_get_unmapped_area() will always check for MAP_FIXED and return that +address. So by the time we do security_mmap_addr(0) things get funky for +shmat(). + +The testcase itself shows that while a regular user crashes, root will not +have a problem attaching a nil-page. There are two possible fixes to +this. The first, and which this patch does, is to simply allow root to +crash as well -- this is also regular mmap behavior, ie when hacking up +the testcase and adding mmap(... |MAP_FIXED). While this approach is the +safer option, the second alternative is to ignore SHM_RND if the rounded +address is 0, thus only having MAP_SHARED flags. This makes the behavior +of shmat() identical to the mmap() case. The downside of this is +obviously user visible, but does make sense in that it maintains semantics +after the round-down wrt 0 address and mmap. + +Passes shm related ltp tests. + +Link: http://lkml.kernel.org/r/1486050195-18629-1-git-send-email-dave@stgolabs.net +Signed-off-by: Davidlohr Bueso +Reported-by: Gareth Evans +Cc: Manfred Spraul +Cc: Michael Kerrisk +Cc: +Signed-off-by: Andrew Morton +--- + ipc/shm.c | 13 +++++++++---- + 1 file changed, 9 insertions(+), 4 deletions(-) + +--- a/ipc/shm.c ++++ b/ipc/shm.c +@@ -1085,8 +1085,8 @@ out_unlock1: + * "raddr" thing points to kernel space, and there has to be a wrapper around + * this. + */ +-long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr, +- unsigned long shmlba) ++long do_shmat(int shmid, char __user *shmaddr, int shmflg, ++ ulong *raddr, unsigned long shmlba) + { + struct shmid_kernel *shp; + unsigned long addr; +@@ -1107,8 +1107,13 @@ long do_shmat(int shmid, char __user *sh + goto out; + else if ((addr = (ulong)shmaddr)) { + if (addr & (shmlba - 1)) { +- if (shmflg & SHM_RND) +- addr &= ~(shmlba - 1); /* round down */ ++ /* ++ * Round down to the nearest multiple of shmlba. ++ * For sane do_mmap_pgoff() parameters, avoid ++ * round downs that trigger nil-page and MAP_FIXED. ++ */ ++ if ((shmflg & SHM_RND) && addr >= shmlba) ++ addr &= ~(shmlba - 1); + else + #ifndef __ARCH_FORCE_SHMLBA + if (addr & ~PAGE_MASK) diff --git a/debian/patches/series b/debian/patches/series index 28509ec98..558b64541 100644 --- a/debian/patches/series +++ b/debian/patches/series @@ -109,6 +109,7 @@ features/all/securelevel/arm64-add-kernel-config-option-to-set-securelevel-wh.pa # Security fixes debian/i386-686-pae-pci-set-pci-nobios-by-default.patch bugfix/x86/kvm-fix-page-struct-leak-in-handle_vmon.patch +bugfix/all/ipc-shm-fix-shmat-mmap-nil-page-protection.patch # Fix exported symbol versions bugfix/ia64/revert-ia64-move-exports-to-definitions.patch