Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753092AbeADMJw (ORCPT + 1 other); Thu, 4 Jan 2018 07:09:52 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:40036 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752948AbeADMJu (ORCPT ); Thu, 4 Jan 2018 07:09:50 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Eric Biggers , Serge Hallyn , James Morris Subject: [PATCH 4.14 02/14] capabilities: fix buffer overread on very short xattr Date: Thu, 4 Jan 2018 13:09:19 +0100 Message-Id: <20180104120917.362003545@linuxfoundation.org> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20180104120917.043667757@linuxfoundation.org> References: <20180104120917.043667757@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Biggers commit dc32b5c3e6e2ef29cef76d9ce1b92d394446150e upstream. If userspace attempted to set a "security.capability" xattr shorter than 4 bytes (e.g. 'setfattr -n security.capability -v x file'), then cap_convert_nscap() read past the end of the buffer containing the xattr value because it accessed the ->magic_etc field without verifying that the xattr value is long enough to contain that field. Fix it by validating the xattr value size first. This bug was found using syzkaller with KASAN. The KASAN report was as follows (cleaned up slightly): BUG: KASAN: slab-out-of-bounds in cap_convert_nscap+0x514/0x630 security/commoncap.c:498 Read of size 4 at addr ffff88002d8741c0 by task syz-executor1/2852 CPU: 0 PID: 2852 Comm: syz-executor1 Not tainted 4.15.0-rc6-00200-gcc0aac99d977 #253 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-20171110_100015-anatol 04/01/2014 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0xe3/0x195 lib/dump_stack.c:53 print_address_description+0x73/0x260 mm/kasan/report.c:252 kasan_report_error mm/kasan/report.c:351 [inline] kasan_report+0x235/0x350 mm/kasan/report.c:409 cap_convert_nscap+0x514/0x630 security/commoncap.c:498 setxattr+0x2bd/0x350 fs/xattr.c:446 path_setxattr+0x168/0x1b0 fs/xattr.c:472 SYSC_setxattr fs/xattr.c:487 [inline] SyS_setxattr+0x36/0x50 fs/xattr.c:483 entry_SYSCALL_64_fastpath+0x18/0x85 Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities") Signed-off-by: Eric Biggers Reviewed-by: Serge Hallyn Signed-off-by: James Morris Signed-off-by: Greg Kroah-Hartman --- security/commoncap.c | 21 +++++++++------------ 1 file changed, 9 insertions(+), 12 deletions(-) --- a/security/commoncap.c +++ b/security/commoncap.c @@ -348,21 +348,18 @@ static __u32 sansflags(__u32 m) return m & ~VFS_CAP_FLAGS_EFFECTIVE; } -static bool is_v2header(size_t size, __le32 magic) +static bool is_v2header(size_t size, const struct vfs_cap_data *cap) { - __u32 m = le32_to_cpu(magic); if (size != XATTR_CAPS_SZ_2) return false; - return sansflags(m) == VFS_CAP_REVISION_2; + return sansflags(le32_to_cpu(cap->magic_etc)) == VFS_CAP_REVISION_2; } -static bool is_v3header(size_t size, __le32 magic) +static bool is_v3header(size_t size, const struct vfs_cap_data *cap) { - __u32 m = le32_to_cpu(magic); - if (size != XATTR_CAPS_SZ_3) return false; - return sansflags(m) == VFS_CAP_REVISION_3; + return sansflags(le32_to_cpu(cap->magic_etc)) == VFS_CAP_REVISION_3; } /* @@ -405,7 +402,7 @@ int cap_inode_getsecurity(struct inode * fs_ns = inode->i_sb->s_user_ns; cap = (struct vfs_cap_data *) tmpbuf; - if (is_v2header((size_t) ret, cap->magic_etc)) { + if (is_v2header((size_t) ret, cap)) { /* If this is sizeof(vfs_cap_data) then we're ok with the * on-disk value, so return that. */ if (alloc) @@ -413,7 +410,7 @@ int cap_inode_getsecurity(struct inode * else kfree(tmpbuf); return ret; - } else if (!is_v3header((size_t) ret, cap->magic_etc)) { + } else if (!is_v3header((size_t) ret, cap)) { kfree(tmpbuf); return -EINVAL; } @@ -470,9 +467,9 @@ static kuid_t rootid_from_xattr(const vo return make_kuid(task_ns, rootid); } -static bool validheader(size_t size, __le32 magic) +static bool validheader(size_t size, const struct vfs_cap_data *cap) { - return is_v2header(size, magic) || is_v3header(size, magic); + return is_v2header(size, cap) || is_v3header(size, cap); } /* @@ -495,7 +492,7 @@ int cap_convert_nscap(struct dentry *den if (!*ivalue) return -EINVAL; - if (!validheader(size, cap->magic_etc)) + if (!validheader(size, cap)) return -EINVAL; if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP)) return -EPERM;