Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933603AbaBUNvZ (ORCPT ); Fri, 21 Feb 2014 08:51:25 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:46836 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932065AbaBUMtv (ORCPT ); Fri, 21 Feb 2014 07:49:51 -0500 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Stephen Smalley , Paul Moore , Luis Henriques Subject: [PATCH 3.11 030/121] SELinux: Fix kernel BUG on empty security contexts. Date: Fri, 21 Feb 2014 12:47:34 +0000 Message-Id: <1392986945-9693-31-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.9.0 In-Reply-To: <1392986945-9693-1-git-send-email-luis.henriques@canonical.com> References: <1392986945-9693-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.11.10.5 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Stephen Smalley commit 2172fa709ab32ca60e86179dc67d0857be8e2c98 upstream. Setting an empty security context (length=0) on a file will lead to incorrectly dereferencing the type and other fields of the security context structure, yielding a kernel BUG. As a zero-length security context is never valid, just reject all such security contexts whether coming from userspace via setxattr or coming from the filesystem upon a getxattr request by SELinux. Setting a security context value (empty or otherwise) unknown to SELinux in the first place is only possible for a root process (CAP_MAC_ADMIN), and, if running SELinux in enforcing mode, only if the corresponding SELinux mac_admin permission is also granted to the domain by policy. In Fedora policies, this is only allowed for specific domains such as livecd for setting down security contexts that are not defined in the build host policy. Reproducer: su setenforce 0 touch foo setfattr -n security.selinux foo Caveat: Relabeling or removing foo after doing the above may not be possible without booting with SELinux disabled. Any subsequent access to foo after doing the above will also trigger the BUG. BUG output from Matthew Thode: [ 473.893141] ------------[ cut here ]------------ [ 473.962110] kernel BUG at security/selinux/ss/services.c:654! [ 473.995314] invalid opcode: 0000 [#6] SMP [ 474.027196] Modules linked in: [ 474.058118] CPU: 0 PID: 8138 Comm: ls Tainted: G D I 3.13.0-grsec #1 [ 474.116637] Hardware name: Supermicro X8ST3/X8ST3, BIOS 2.0 07/29/10 [ 474.149768] task: ffff8805f50cd010 ti: ffff8805f50cd488 task.ti: ffff8805f50cd488 [ 474.183707] RIP: 0010:[] [] context_struct_compute_av+0xce/0x308 [ 474.219954] RSP: 0018:ffff8805c0ac3c38 EFLAGS: 00010246 [ 474.252253] RAX: 0000000000000000 RBX: ffff8805c0ac3d94 RCX: 0000000000000100 [ 474.287018] RDX: ffff8805e8aac000 RSI: 00000000ffffffff RDI: ffff8805e8aaa000 [ 474.321199] RBP: ffff8805c0ac3cb8 R08: 0000000000000010 R09: 0000000000000006 [ 474.357446] R10: 0000000000000000 R11: ffff8805c567a000 R12: 0000000000000006 [ 474.419191] R13: ffff8805c2b74e88 R14: 00000000000001da R15: 0000000000000000 [ 474.453816] FS: 00007f2e75220800(0000) GS:ffff88061fc00000(0000) knlGS:0000000000000000 [ 474.489254] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 474.522215] CR2: 00007f2e74716090 CR3: 00000005c085e000 CR4: 00000000000207f0 [ 474.556058] Stack: [ 474.584325] ffff8805c0ac3c98 ffffffff811b549b ffff8805c0ac3c98 ffff8805f1190a40 [ 474.618913] ffff8805a6202f08 ffff8805c2b74e88 00068800d0464990 ffff8805e8aac860 [ 474.653955] ffff8805c0ac3cb8 000700068113833a ffff880606c75060 ffff8805c0ac3d94 [ 474.690461] Call Trace: [ 474.723779] [] ? lookup_fast+0x1cd/0x22a [ 474.778049] [] security_compute_av+0xf4/0x20b [ 474.811398] [] avc_compute_av+0x2a/0x179 [ 474.843813] [] avc_has_perm+0x45/0xf4 [ 474.875694] [] inode_has_perm+0x2a/0x31 [ 474.907370] [] selinux_inode_getattr+0x3c/0x3e [ 474.938726] [] security_inode_getattr+0x1b/0x22 [ 474.970036] [] vfs_getattr+0x19/0x2d [ 475.000618] [] vfs_fstatat+0x54/0x91 [ 475.030402] [] vfs_lstat+0x19/0x1b [ 475.061097] [] SyS_newlstat+0x15/0x30 [ 475.094595] [] ? __audit_syscall_entry+0xa1/0xc3 [ 475.148405] [] system_call_fastpath+0x16/0x1b [ 475.179201] Code: 00 48 85 c0 48 89 45 b8 75 02 0f 0b 48 8b 45 a0 48 8b 3d 45 d0 b6 00 8b 40 08 89 c6 ff ce e8 d1 b0 06 00 48 85 c0 49 89 c7 75 02 <0f> 0b 48 8b 45 b8 4c 8b 28 eb 1e 49 8d 7d 08 be 80 01 00 00 e8 [ 475.255884] RIP [] context_struct_compute_av+0xce/0x308 [ 475.296120] RSP [ 475.328734] ---[ end trace f076482e9d754adc ]--- Reported-by: Matthew Thode Signed-off-by: Stephen Smalley Signed-off-by: Paul Moore Signed-off-by: Luis Henriques --- security/selinux/ss/services.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c index b4feecc..18caa16 100644 --- a/security/selinux/ss/services.c +++ b/security/selinux/ss/services.c @@ -1231,6 +1231,10 @@ static int security_context_to_sid_core(const char *scontext, u32 scontext_len, struct context context; int rc = 0; + /* An empty security context is never valid. */ + if (!scontext_len) + return -EINVAL; + if (!ss_initialized) { int i; -- 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/