1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
|
Bugzilla: 1013466
Upstream-status: 3.15 (commit 98883bfd9d603a2760f6d53eccfaa3ae2c053e72)
It turns out that doing the SELinux MAC checks for mmap() before the
DAC checks was causing users and the SELinux policy folks headaches
as users were seeing a lot of SELinux AVC denials for the
memprotect:mmap_zero permission that would have also been denied by
the normal DAC capability checks (CAP_SYS_RAWIO).
Example:
# cat mmap_test.c
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <sys/mman.h>
int main(int argc, char *argv[])
{
int rc;
void *mem;
mem = mmap(0x0, 4096,
PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
if (mem == MAP_FAILED)
return errno;
printf("mem = %p\n", mem);
munmap(mem, 4096);
return 0;
}
# gcc -g -O0 -o mmap_test mmap_test.c
# ./mmap_test
mem = (nil)
# ausearch -m AVC | grep mmap_zero
type=AVC msg=audit(...): avc: denied { mmap_zero }
for pid=1025 comm="mmap_test"
scontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
tcontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
tclass=memprotect
This patch corrects things so that when the above example is run by a
user without CAP_SYS_RAWIO the SELinux AVC is no longer generated as
the DAC capability check fails before the SELinux permission check.
Signed-off-by: Paul Moore <pmoore@redhat.com>
---
security/selinux/hooks.c | 20 ++++++++------------
1 file changed, 8 insertions(+), 12 deletions(-)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 57b0b49..e3664ae 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3205,24 +3205,20 @@ error:
static int selinux_mmap_addr(unsigned long addr)
{
- int rc = 0;
- u32 sid = current_sid();
+ int rc;
+
+ /* do DAC check on address space usage */
+ rc = cap_mmap_addr(addr);
+ if (rc)
+ return rc;
- /*
- * notice that we are intentionally putting the SELinux check before
- * the secondary cap_file_mmap check. This is such a likely attempt
- * at bad behaviour/exploit that we always want to get the AVC, even
- * if DAC would have also denied the operation.
- */
if (addr < CONFIG_LSM_MMAP_MIN_ADDR) {
+ u32 sid = current_sid();
rc = avc_has_perm(sid, sid, SECCLASS_MEMPROTECT,
MEMPROTECT__MMAP_ZERO, NULL);
- if (rc)
- return rc;
}
- /* do DAC check on address space usage */
- return cap_mmap_addr(addr);
+ return rc;
}
static int selinux_mmap_file(struct file *file, unsigned long reqprot,
_______________________________________________
Selinux mailing list
Selinux@tycho.nsa.gov
To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
To get help, send an email containing "help" to Selinux-request@tycho.nsa.gov.
|
