CVE-2014-1874 SELinux: local denial of service (rhbz 1062356 1062507)
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Josh Boyer
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From 2172fa709ab32ca60e86179dc67d0857be8e2c98 Mon Sep 17 00:00:00 2001
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From: Stephen Smalley <sds@tycho.nsa.gov>
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Date: Thu, 30 Jan 2014 11:26:59 -0500
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Subject: [PATCH] SELinux: Fix kernel BUG on empty security contexts.
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Setting an empty security context (length=0) on a file will
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lead to incorrectly dereferencing the type and other fields
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of the security context structure, yielding a kernel BUG.
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As a zero-length security context is never valid, just reject
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all such security contexts whether coming from userspace
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via setxattr or coming from the filesystem upon a getxattr
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request by SELinux.
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Setting a security context value (empty or otherwise) unknown to
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SELinux in the first place is only possible for a root process
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(CAP_MAC_ADMIN), and, if running SELinux in enforcing mode, only
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if the corresponding SELinux mac_admin permission is also granted
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to the domain by policy. In Fedora policies, this is only allowed for
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specific domains such as livecd for setting down security contexts
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that are not defined in the build host policy.
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Reproducer:
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su
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setenforce 0
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touch foo
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setfattr -n security.selinux foo
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Caveat:
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Relabeling or removing foo after doing the above may not be possible
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without booting with SELinux disabled. Any subsequent access to foo
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after doing the above will also trigger the BUG.
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BUG output from Matthew Thode:
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[ 473.893141] ------------[ cut here ]------------
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[ 473.962110] kernel BUG at security/selinux/ss/services.c:654!
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[ 473.995314] invalid opcode: 0000 [#6] SMP
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[ 474.027196] Modules linked in:
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[ 474.058118] CPU: 0 PID: 8138 Comm: ls Tainted: G D I
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3.13.0-grsec #1
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[ 474.116637] Hardware name: Supermicro X8ST3/X8ST3, BIOS 2.0
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07/29/10
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[ 474.149768] task: ffff8805f50cd010 ti: ffff8805f50cd488 task.ti:
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ffff8805f50cd488
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[ 474.183707] RIP: 0010:[<ffffffff814681c7>] [<ffffffff814681c7>]
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context_struct_compute_av+0xce/0x308
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[ 474.219954] RSP: 0018:ffff8805c0ac3c38 EFLAGS: 00010246
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[ 474.252253] RAX: 0000000000000000 RBX: ffff8805c0ac3d94 RCX:
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0000000000000100
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[ 474.287018] RDX: ffff8805e8aac000 RSI: 00000000ffffffff RDI:
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ffff8805e8aaa000
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[ 474.321199] RBP: ffff8805c0ac3cb8 R08: 0000000000000010 R09:
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0000000000000006
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[ 474.357446] R10: 0000000000000000 R11: ffff8805c567a000 R12:
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0000000000000006
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[ 474.419191] R13: ffff8805c2b74e88 R14: 00000000000001da R15:
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0000000000000000
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[ 474.453816] FS: 00007f2e75220800(0000) GS:ffff88061fc00000(0000)
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knlGS:0000000000000000
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[ 474.489254] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
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[ 474.522215] CR2: 00007f2e74716090 CR3: 00000005c085e000 CR4:
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00000000000207f0
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[ 474.556058] Stack:
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[ 474.584325] ffff8805c0ac3c98 ffffffff811b549b ffff8805c0ac3c98
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ffff8805f1190a40
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[ 474.618913] ffff8805a6202f08 ffff8805c2b74e88 00068800d0464990
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ffff8805e8aac860
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[ 474.653955] ffff8805c0ac3cb8 000700068113833a ffff880606c75060
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ffff8805c0ac3d94
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[ 474.690461] Call Trace:
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[ 474.723779] [<ffffffff811b549b>] ? lookup_fast+0x1cd/0x22a
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[ 474.778049] [<ffffffff81468824>] security_compute_av+0xf4/0x20b
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[ 474.811398] [<ffffffff8196f419>] avc_compute_av+0x2a/0x179
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[ 474.843813] [<ffffffff8145727b>] avc_has_perm+0x45/0xf4
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[ 474.875694] [<ffffffff81457d0e>] inode_has_perm+0x2a/0x31
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[ 474.907370] [<ffffffff81457e76>] selinux_inode_getattr+0x3c/0x3e
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[ 474.938726] [<ffffffff81455cf6>] security_inode_getattr+0x1b/0x22
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[ 474.970036] [<ffffffff811b057d>] vfs_getattr+0x19/0x2d
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[ 475.000618] [<ffffffff811b05e5>] vfs_fstatat+0x54/0x91
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[ 475.030402] [<ffffffff811b063b>] vfs_lstat+0x19/0x1b
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[ 475.061097] [<ffffffff811b077e>] SyS_newlstat+0x15/0x30
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[ 475.094595] [<ffffffff8113c5c1>] ? __audit_syscall_entry+0xa1/0xc3
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[ 475.148405] [<ffffffff8197791e>] system_call_fastpath+0x16/0x1b
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[ 475.179201] Code: 00 48 85 c0 48 89 45 b8 75 02 0f 0b 48 8b 45 a0 48
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8b 3d 45 d0 b6 00 8b 40 08 89 c6 ff ce e8 d1 b0 06 00 48 85 c0 49 89 c7
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75 02 <0f> 0b 48 8b 45 b8 4c 8b 28 eb 1e 49 8d 7d 08 be 80 01 00 00 e8
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[ 475.255884] RIP [<ffffffff814681c7>]
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context_struct_compute_av+0xce/0x308
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[ 475.296120] RSP <ffff8805c0ac3c38>
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[ 475.328734] ---[ end trace f076482e9d754adc ]---
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Reported-by: Matthew Thode <mthode@mthode.org>
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Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
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Cc: stable@vger.kernel.org
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Signed-off-by: Paul Moore <pmoore@redhat.com>
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---
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security/selinux/ss/services.c | 4 ++++
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1 file changed, 4 insertions(+)
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diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
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index fc5a63a..f1e46d7 100644
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--- a/security/selinux/ss/services.c
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+++ b/security/selinux/ss/services.c
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@@ -1232,6 +1232,10 @@ static int security_context_to_sid_core(const char *scontext, u32 scontext_len,
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struct context context;
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int rc = 0;
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+ /* An empty security context is never valid. */
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+ if (!scontext_len)
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+ return -EINVAL;
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+
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if (!ss_initialized) {
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int i;
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--
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1.8.5.3
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@ -750,6 +750,9 @@ Patch25186: ath9k_htc-make-sta_rc_update-atomic-for-most-calls.patch
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#rhbz 950630
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Patch25187: xhci-fix-resume-issues-on-renesas-chips-in-samsung-laptops.patch
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#CVE-2014-1874 rhbz 1062356 1062507
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Patch25188: SELinux-Fix-kernel-BUG-on-empty-security-contexts.patch
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# END OF PATCH DEFINITIONS
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%endif
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@ -1456,6 +1459,9 @@ ApplyPatch ath9k_htc-make-sta_rc_update-atomic-for-most-calls.patch
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#rhbz 950630
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ApplyPatch xhci-fix-resume-issues-on-renesas-chips-in-samsung-laptops.patch
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#CVE-2014-1874 rhbz 1062356 1062507
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ApplyPatch SELinux-Fix-kernel-BUG-on-empty-security-contexts.patch
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# END OF PATCH APPLICATIONS
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%endif
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@ -2267,6 +2273,9 @@ fi
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# ||----w |
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# || ||
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%changelog
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* Wed Feb 12 2014 Josh Boyer <jwboyer@fedoraproject.org>
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- CVE-2014-1874 SELinux: local denial of service (rhbz 1062356 1062507)
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* Wed Feb 12 2014 Justin M. Forbes <jforbes@fedoraproject.org> - 3.13.2-200
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- Packaging fixes for tmon and trace
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