Revision 2172fa709ab32ca60e86179dc67d0857be8e2c98 authored by Stephen Smalley on 30 January 2014, 16:26:59 UTC, committed by Paul Moore on 05 February 2014, 17:20:51 UTC
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:[<ffffffff814681c7>]  [<ffffffff814681c7>]
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]  [<ffffffff811b549b>] ? lookup_fast+0x1cd/0x22a
[  474.778049]  [<ffffffff81468824>] security_compute_av+0xf4/0x20b
[  474.811398]  [<ffffffff8196f419>] avc_compute_av+0x2a/0x179
[  474.843813]  [<ffffffff8145727b>] avc_has_perm+0x45/0xf4
[  474.875694]  [<ffffffff81457d0e>] inode_has_perm+0x2a/0x31
[  474.907370]  [<ffffffff81457e76>] selinux_inode_getattr+0x3c/0x3e
[  474.938726]  [<ffffffff81455cf6>] security_inode_getattr+0x1b/0x22
[  474.970036]  [<ffffffff811b057d>] vfs_getattr+0x19/0x2d
[  475.000618]  [<ffffffff811b05e5>] vfs_fstatat+0x54/0x91
[  475.030402]  [<ffffffff811b063b>] vfs_lstat+0x19/0x1b
[  475.061097]  [<ffffffff811b077e>] SyS_newlstat+0x15/0x30
[  475.094595]  [<ffffffff8113c5c1>] ? __audit_syscall_entry+0xa1/0xc3
[  475.148405]  [<ffffffff8197791e>] 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  [<ffffffff814681c7>]
context_struct_compute_av+0xce/0x308
[  475.296120]  RSP <ffff8805c0ac3c38>
[  475.328734] ---[ end trace f076482e9d754adc ]---

Reported-by:  Matthew Thode <mthode@mthode.org>
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Cc: stable@vger.kernel.org
Signed-off-by: Paul Moore <pmoore@redhat.com>
1 parent 6a96e15
Raw File
Makefile
include scripts/Makefile.include

help:
	@echo 'Possible targets:'
	@echo ''
	@echo '  cgroup     - cgroup tools'
	@echo '  cpupower   - a tool for all things x86 CPU power'
	@echo '  firewire   - the userspace part of nosy, an IEEE-1394 traffic sniffer'
	@echo '  lguest     - a minimal 32-bit x86 hypervisor'
	@echo '  perf       - Linux performance measurement and analysis tool'
	@echo '  selftests  - various kernel selftests'
	@echo '  turbostat  - Intel CPU idle stats and freq reporting tool'
	@echo '  usb        - USB testing tools'
	@echo '  virtio     - vhost test module'
	@echo '  net        - misc networking tools'
	@echo '  vm         - misc vm tools'
	@echo '  x86_energy_perf_policy - Intel energy policy tool'
	@echo '  tmon       - thermal monitoring and tuning tool'
	@echo ''
	@echo 'You can do:'
	@echo ' $$ make -C tools/ <tool>_install'
	@echo ''
	@echo '  from the kernel command line to build and install one of'
	@echo '  the tools above'
	@echo ''
	@echo '  $$ make tools/install'
	@echo ''
	@echo '  installs all tools.'
	@echo ''
	@echo 'Cleaning targets:'
	@echo ''
	@echo '  all of the above with the "_clean" string appended cleans'
	@echo '    the respective build directory.'
	@echo '  clean: a summary clean target to clean _all_ folders'

cpupower: FORCE
	$(call descend,power/$@)

cgroup firewire guest usb virtio vm net: FORCE
	$(call descend,$@)

liblk: FORCE
	$(call descend,lib/lk)

perf: liblk FORCE
	$(call descend,$@)

selftests: FORCE
	$(call descend,testing/$@)

turbostat x86_energy_perf_policy: FORCE
	$(call descend,power/x86/$@)

tmon: FORCE
	$(call descend,thermal/$@)

cpupower_install:
	$(call descend,power/$(@:_install=),install)

cgroup_install firewire_install lguest_install perf_install usb_install virtio_install vm_install net_install:
	$(call descend,$(@:_install=),install)

selftests_install:
	$(call descend,testing/$(@:_clean=),install)

turbostat_install x86_energy_perf_policy_install:
	$(call descend,power/x86/$(@:_install=),install)

tmon_install:
	$(call descend,thermal/$(@:_install=),install)

install: cgroup_install cpupower_install firewire_install lguest_install \
		perf_install selftests_install turbostat_install usb_install \
		virtio_install vm_install net_install x86_energy_perf_policy_install \
	tmon

cpupower_clean:
	$(call descend,power/cpupower,clean)

cgroup_clean firewire_clean lguest_clean usb_clean virtio_clean vm_clean net_clean:
	$(call descend,$(@:_clean=),clean)

liblk_clean:
	$(call descend,lib/lk,clean)

perf_clean: liblk_clean
	$(call descend,$(@:_clean=),clean)

selftests_clean:
	$(call descend,testing/$(@:_clean=),clean)

turbostat_clean x86_energy_perf_policy_clean:
	$(call descend,power/x86/$(@:_clean=),clean)

tmon_clean:
	$(call descend,thermal/tmon,clean)

clean: cgroup_clean cpupower_clean firewire_clean lguest_clean perf_clean \
		selftests_clean turbostat_clean usb_clean virtio_clean \
		vm_clean net_clean x86_energy_perf_policy_clean tmon_clean

.PHONY: FORCE
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