* [PATCH] acpi: fix a potential inconsistency caused by double-fetch
@ 2018-12-25 21:46 Kangjie Lu
2018-12-25 22:20 ` kbuild test robot
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Kangjie Lu @ 2018-12-25 21:46 UTC (permalink / raw)
To: kjlu; +Cc: pakki001, Rafael J. Wysocki, Len Brown, linux-acpi, linux-kernel
"user_buf->length" is in user space, and copied in twice. The second
copy is after it passes the security check. If a user program races to
change user_buf->length in user space, the data fetched in the second
copy may invalidate the security check. The fix avoids the double-fetch
issue by using the value passing the security check.
Signed-off-by: Kangjie Lu <kjlu@umn.edu>
---
drivers/acpi/custom_method.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
index 4451877f83b6..f75f664301b3 100644
--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -26,17 +26,16 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
static u32 max_size;
static u32 uncopied_bytes;
- struct acpi_table_header table;
acpi_status status;
if (!(*ppos)) {
/* parse the table header to get the table length */
if (count <= sizeof(struct acpi_table_header))
return -EINVAL;
- if (copy_from_user(&table, user_buf,
- sizeof(struct acpi_table_header)))
+ if (get_user(max_size,
+ &(struct acpi_table_header *)user_buf->length))
return -EFAULT;
- uncopied_bytes = max_size = table.length;
+ uncopied_bytes = max_size;
buf = kzalloc(max_size, GFP_KERNEL);
if (!buf)
return -ENOMEM;
@@ -56,6 +55,8 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
buf = NULL;
return -EFAULT;
}
+ /* Ensure table length is not changed in the second copy */
+ (struct acpi_table_header *)(buf + (*ppos))->length = max_size;
uncopied_bytes -= count;
*ppos += count;
--
2.17.2 (Apple Git-113)
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] acpi: fix a potential inconsistency caused by double-fetch
2018-12-25 21:46 [PATCH] acpi: fix a potential inconsistency caused by double-fetch Kangjie Lu
@ 2018-12-25 22:20 ` kbuild test robot
2018-12-26 0:11 ` kbuild test robot
2019-01-09 8:14 ` [PATCH v2] " Kangjie Lu
2 siblings, 0 replies; 6+ messages in thread
From: kbuild test robot @ 2018-12-25 22:20 UTC (permalink / raw)
To: Kangjie Lu
Cc: kbuild-all, kjlu, pakki001, Rafael J. Wysocki, Len Brown,
linux-acpi, linux-kernel
[-- Attachment #1: Type: text/plain, Size: 5488 bytes --]
Hi Kangjie,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on pm/linux-next]
[also build test ERROR on v4.20 next-20181224]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Kangjie-Lu/acpi-fix-a-potential-inconsistency-caused-by-double-fetch/20181226-054721
base: https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next
config: x86_64-randconfig-x019-201851 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
# save the attached .config to linux build tree
make ARCH=x86_64
All error/warnings (new ones prefixed by >>):
In file included from include/linux/uaccess.h:14:0,
from drivers//acpi/custom_method.c:8:
drivers//acpi/custom_method.c: In function 'cm_write':
>> drivers//acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
arch/x86/include/asm/uaccess.h:138:41: note: in definition of macro '__inttype'
__typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
^
>> drivers//acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
arch/x86/include/asm/uaccess.h:138:12: error: first argument to '__builtin_choose_expr' not a constant
__typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
^
arch/x86/include/asm/uaccess.h:174:11: note: in expansion of macro '__inttype'
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
^~~~~~~~~
>> drivers//acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
>> drivers//acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
arch/x86/include/asm/uaccess.h:180:15: note: in definition of macro 'get_user'
: "0" (ptr), "i" (sizeof(*(ptr)))); \
^~~
>> drivers//acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
arch/x86/include/asm/uaccess.h:180:35: note: in definition of macro 'get_user'
: "0" (ptr), "i" (sizeof(*(ptr)))); \
^~~
>> drivers//acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
arch/x86/include/asm/uaccess.h:181:30: note: in definition of macro 'get_user'
(x) = (__force __typeof__(*(ptr))) __val_gu; \
^~~
drivers//acpi/custom_method.c:59:45: error: request for member 'length' in something not a structure or union
(struct acpi_table_header *)(buf + (*ppos))->length = max_size;
^~
vim +/get_user +35 drivers//acpi/custom_method.c
> 8 #include <linux/uaccess.h>
9 #include <linux/debugfs.h>
10 #include <linux/acpi.h>
11
12 #include "internal.h"
13
14 #define _COMPONENT ACPI_SYSTEM_COMPONENT
15 ACPI_MODULE_NAME("custom_method");
16 MODULE_LICENSE("GPL");
17
18 static struct dentry *cm_dentry;
19
20 /* /sys/kernel/debug/acpi/custom_method */
21
22 static ssize_t cm_write(struct file *file, const char __user * user_buf,
23 size_t count, loff_t *ppos)
24 {
25 static char *buf;
26 static u32 max_size;
27 static u32 uncopied_bytes;
28
29 acpi_status status;
30
31 if (!(*ppos)) {
32 /* parse the table header to get the table length */
33 if (count <= sizeof(struct acpi_table_header))
34 return -EINVAL;
> 35 if (get_user(max_size,
> 36 &(struct acpi_table_header *)user_buf->length))
37 return -EFAULT;
38 uncopied_bytes = max_size;
39 buf = kzalloc(max_size, GFP_KERNEL);
40 if (!buf)
41 return -ENOMEM;
42 }
43
44 if (buf == NULL)
45 return -EINVAL;
46
47 if ((*ppos > max_size) ||
48 (*ppos + count > max_size) ||
49 (*ppos + count < count) ||
50 (count > uncopied_bytes))
51 return -EINVAL;
52
53 if (copy_from_user(buf + (*ppos), user_buf, count)) {
54 kfree(buf);
55 buf = NULL;
56 return -EFAULT;
57 }
58 /* Ensure table length is not changed in the second copy */
59 (struct acpi_table_header *)(buf + (*ppos))->length = max_size;
60
61 uncopied_bytes -= count;
62 *ppos += count;
63
64 if (!uncopied_bytes) {
65 status = acpi_install_method(buf);
66 kfree(buf);
67 buf = NULL;
68 if (ACPI_FAILURE(status))
69 return -EINVAL;
70 add_taint(TAINT_OVERRIDDEN_ACPI_TABLE, LOCKDEP_NOW_UNRELIABLE);
71 }
72
73 return count;
74 }
75
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 28829 bytes --]
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] acpi: fix a potential inconsistency caused by double-fetch
2018-12-25 21:46 [PATCH] acpi: fix a potential inconsistency caused by double-fetch Kangjie Lu
2018-12-25 22:20 ` kbuild test robot
@ 2018-12-26 0:11 ` kbuild test robot
2019-01-09 8:14 ` [PATCH v2] " Kangjie Lu
2 siblings, 0 replies; 6+ messages in thread
From: kbuild test robot @ 2018-12-26 0:11 UTC (permalink / raw)
To: Kangjie Lu
Cc: kbuild-all, kjlu, pakki001, Rafael J. Wysocki, Len Brown,
linux-acpi, linux-kernel
[-- Attachment #1: Type: text/plain, Size: 13513 bytes --]
Hi Kangjie,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on pm/linux-next]
[also build test WARNING on v4.20 next-20181224]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Kangjie-Lu/acpi-fix-a-potential-inconsistency-caused-by-double-fetch/20181226-054721
base: https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next
config: i386-randconfig-c0-12260412 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
All warnings (new ones prefixed by >>):
In file included from include/linux/init.h:5:0,
from drivers/acpi/custom_method.c:5:
drivers/acpi/custom_method.c: In function 'cm_write':
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:58:30: note: in definition of macro '__trace_if'
if (__builtin_constant_p(!!(cond)) ? !!(cond) : \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
arch/x86/include/asm/uaccess.h:174:11: note: in expansion of macro '__inttype'
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
^~~~~~~~~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
arch/x86/include/asm/uaccess.h:138:12: error: first argument to '__builtin_choose_expr' not a constant
__typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
^
include/linux/compiler.h:58:30: note: in definition of macro '__trace_if'
if (__builtin_constant_p(!!(cond)) ? !!(cond) : \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
arch/x86/include/asm/uaccess.h:174:11: note: in expansion of macro '__inttype'
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
^~~~~~~~~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:58:30: note: in definition of macro '__trace_if'
if (__builtin_constant_p(!!(cond)) ? !!(cond) : \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:58:30: note: in definition of macro '__trace_if'
if (__builtin_constant_p(!!(cond)) ? !!(cond) : \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:58:30: note: in definition of macro '__trace_if'
if (__builtin_constant_p(!!(cond)) ? !!(cond) : \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:58:42: note: in definition of macro '__trace_if'
if (__builtin_constant_p(!!(cond)) ? !!(cond) : \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
arch/x86/include/asm/uaccess.h:174:11: note: in expansion of macro '__inttype'
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
^~~~~~~~~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
arch/x86/include/asm/uaccess.h:138:12: error: first argument to '__builtin_choose_expr' not a constant
__typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
^
include/linux/compiler.h:58:42: note: in definition of macro '__trace_if'
if (__builtin_constant_p(!!(cond)) ? !!(cond) : \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
arch/x86/include/asm/uaccess.h:174:11: note: in expansion of macro '__inttype'
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
^~~~~~~~~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:58:42: note: in definition of macro '__trace_if'
if (__builtin_constant_p(!!(cond)) ? !!(cond) : \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:58:42: note: in definition of macro '__trace_if'
if (__builtin_constant_p(!!(cond)) ? !!(cond) : \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:58:42: note: in definition of macro '__trace_if'
if (__builtin_constant_p(!!(cond)) ? !!(cond) : \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:69:16: note: in definition of macro '__trace_if'
______r = !!(cond); \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
arch/x86/include/asm/uaccess.h:174:11: note: in expansion of macro '__inttype'
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
^~~~~~~~~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
arch/x86/include/asm/uaccess.h:138:12: error: first argument to '__builtin_choose_expr' not a constant
__typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
^
include/linux/compiler.h:69:16: note: in definition of macro '__trace_if'
______r = !!(cond); \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
arch/x86/include/asm/uaccess.h:174:11: note: in expansion of macro '__inttype'
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
^~~~~~~~~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:69:16: note: in definition of macro '__trace_if'
______r = !!(cond); \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:69:16: note: in definition of macro '__trace_if'
______r = !!(cond); \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:36:42: error: request for member 'length' in something not a structure or union
&(struct acpi_table_header *)user_buf->length))
^
include/linux/compiler.h:69:16: note: in definition of macro '__trace_if'
______r = !!(cond); \
^~~~
>> drivers/acpi/custom_method.c:35:3: note: in expansion of macro 'if'
if (get_user(max_size,
^~
drivers/acpi/custom_method.c:35:7: note: in expansion of macro 'get_user'
if (get_user(max_size,
^~~~~~~~
drivers/acpi/custom_method.c:59:45: error: request for member 'length' in something not a structure or union
(struct acpi_table_header *)(buf + (*ppos))->length = max_size;
^~
vim +/if +35 drivers/acpi/custom_method.c
> 5 #include <linux/init.h>
6 #include <linux/module.h>
7 #include <linux/kernel.h>
8 #include <linux/uaccess.h>
9 #include <linux/debugfs.h>
10 #include <linux/acpi.h>
11
12 #include "internal.h"
13
14 #define _COMPONENT ACPI_SYSTEM_COMPONENT
15 ACPI_MODULE_NAME("custom_method");
16 MODULE_LICENSE("GPL");
17
18 static struct dentry *cm_dentry;
19
20 /* /sys/kernel/debug/acpi/custom_method */
21
22 static ssize_t cm_write(struct file *file, const char __user * user_buf,
23 size_t count, loff_t *ppos)
24 {
25 static char *buf;
26 static u32 max_size;
27 static u32 uncopied_bytes;
28
29 acpi_status status;
30
31 if (!(*ppos)) {
32 /* parse the table header to get the table length */
33 if (count <= sizeof(struct acpi_table_header))
34 return -EINVAL;
> 35 if (get_user(max_size,
36 &(struct acpi_table_header *)user_buf->length))
37 return -EFAULT;
38 uncopied_bytes = max_size;
39 buf = kzalloc(max_size, GFP_KERNEL);
40 if (!buf)
41 return -ENOMEM;
42 }
43
44 if (buf == NULL)
45 return -EINVAL;
46
47 if ((*ppos > max_size) ||
48 (*ppos + count > max_size) ||
49 (*ppos + count < count) ||
50 (count > uncopied_bytes))
51 return -EINVAL;
52
53 if (copy_from_user(buf + (*ppos), user_buf, count)) {
54 kfree(buf);
55 buf = NULL;
56 return -EFAULT;
57 }
58 /* Ensure table length is not changed in the second copy */
59 (struct acpi_table_header *)(buf + (*ppos))->length = max_size;
60
61 uncopied_bytes -= count;
62 *ppos += count;
63
64 if (!uncopied_bytes) {
65 status = acpi_install_method(buf);
66 kfree(buf);
67 buf = NULL;
68 if (ACPI_FAILURE(status))
69 return -EINVAL;
70 add_taint(TAINT_OVERRIDDEN_ACPI_TABLE, LOCKDEP_NOW_UNRELIABLE);
71 }
72
73 return count;
74 }
75
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 28333 bytes --]
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v2] acpi: fix a potential inconsistency caused by double-fetch
2018-12-25 21:46 [PATCH] acpi: fix a potential inconsistency caused by double-fetch Kangjie Lu
2018-12-25 22:20 ` kbuild test robot
2018-12-26 0:11 ` kbuild test robot
@ 2019-01-09 8:14 ` Kangjie Lu
2019-01-14 11:15 ` Rafael J. Wysocki
2 siblings, 1 reply; 6+ messages in thread
From: Kangjie Lu @ 2019-01-09 8:14 UTC (permalink / raw)
To: kjlu; +Cc: pakki001, Rafael J. Wysocki, Len Brown, linux-acpi, linux-kernel
"user_buf->length" is in user space, and copied in twice. The second
copy is after it passes the security check. If a user program races to
change user_buf->length in user space, the data fetched in the second
copy may invalidate the security check. The fix avoids the double-fetch
issue by using the value passing the security check.
Signed-off-by: Kangjie Lu <kjlu@umn.edu>
---
drivers/acpi/custom_method.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
index 4451877f83b6..f10ee0519033 100644
--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -26,17 +26,16 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
static u32 max_size;
static u32 uncopied_bytes;
- struct acpi_table_header table;
acpi_status status;
if (!(*ppos)) {
/* parse the table header to get the table length */
if (count <= sizeof(struct acpi_table_header))
return -EINVAL;
- if (copy_from_user(&table, user_buf,
- sizeof(struct acpi_table_header)))
+ if (get_user(max_size,
+ &((struct acpi_table_header *)user_buf)->length))
return -EFAULT;
- uncopied_bytes = max_size = table.length;
+ uncopied_bytes = max_size;
buf = kzalloc(max_size, GFP_KERNEL);
if (!buf)
return -ENOMEM;
@@ -57,6 +56,9 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
return -EFAULT;
}
+ /* Ensure table length is not changed in the second copy */
+ ((struct acpi_table_header *)(buf + (*ppos)))->length = max_size;
+
uncopied_bytes -= count;
*ppos += count;
--
2.17.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v2] acpi: fix a potential inconsistency caused by double-fetch
2019-01-09 8:14 ` [PATCH v2] " Kangjie Lu
@ 2019-01-14 11:15 ` Rafael J. Wysocki
[not found] ` <CAK8KejpGipqLpR93=ZnRze9FU7q5ZhJrGQV33czZwuxqSs0AyQ@mail.gmail.com>
0 siblings, 1 reply; 6+ messages in thread
From: Rafael J. Wysocki @ 2019-01-14 11:15 UTC (permalink / raw)
To: Kangjie Lu
Cc: pakki001, Rafael J. Wysocki, Len Brown, ACPI Devel Maling List,
Linux Kernel Mailing List
On Wed, Jan 9, 2019 at 9:14 AM Kangjie Lu <kjlu@umn.edu> wrote:
>
> "user_buf->length" is in user space, and copied in twice. The second
> copy is after it passes the security check. If a user program races to
> change user_buf->length in user space, the data fetched in the second
> copy may invalidate the security check. The fix avoids the double-fetch
> issue by using the value passing the security check.
AFAICS the patch really does two things: it avoids the issue described
above and avoids using the (redundant) 'table' local variable on the
stack. Arguably, you could fix the issue without getting rid of the
redundant variable.
>
> Signed-off-by: Kangjie Lu <kjlu@umn.edu>
> ---
> drivers/acpi/custom_method.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
> index 4451877f83b6..f10ee0519033 100644
> --- a/drivers/acpi/custom_method.c
> +++ b/drivers/acpi/custom_method.c
> @@ -26,17 +26,16 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
> static u32 max_size;
> static u32 uncopied_bytes;
>
> - struct acpi_table_header table;
> acpi_status status;
>
> if (!(*ppos)) {
> /* parse the table header to get the table length */
> if (count <= sizeof(struct acpi_table_header))
> return -EINVAL;
> - if (copy_from_user(&table, user_buf,
> - sizeof(struct acpi_table_header)))
> + if (get_user(max_size,
> + &((struct acpi_table_header *)user_buf)->length))
> return -EFAULT;
> - uncopied_bytes = max_size = table.length;
> + uncopied_bytes = max_size;
> buf = kzalloc(max_size, GFP_KERNEL);
> if (!buf)
> return -ENOMEM;
> @@ -57,6 +56,9 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
> return -EFAULT;
> }
>
> + /* Ensure table length is not changed in the second copy */
> + ((struct acpi_table_header *)(buf + (*ppos)))->length = max_size;
Why don't you return -EFAULT if max_size is different from ->length?
Surely, the table should not be used at all in that case.
Moreover, wouldn't it be even better to compare the entire header with
the one read previously and return -EFAULT if they don't match?
> +
> uncopied_bytes -= count;
> *ppos += count;
>
> --
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] acpi: fix a potential inconsistency caused by double-fetch
[not found] ` <CAK8KejpGipqLpR93=ZnRze9FU7q5ZhJrGQV33czZwuxqSs0AyQ@mail.gmail.com>
@ 2019-01-15 19:05 ` Rafael J. Wysocki
0 siblings, 0 replies; 6+ messages in thread
From: Rafael J. Wysocki @ 2019-01-15 19:05 UTC (permalink / raw)
To: Kangjie Lu
Cc: Rafael J. Wysocki, Aditya Pakki, Rafael J. Wysocki, Len Brown,
ACPI Devel Maling List, Linux Kernel Mailing List
On Tue, Jan 15, 2019 at 7:05 AM Kangjie Lu <kjlu@umn.edu> wrote:
>
>
>
> On Mon, Jan 14, 2019 at 5:15 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
>>
>> On Wed, Jan 9, 2019 at 9:14 AM Kangjie Lu <kjlu@umn.edu> wrote:
>> >
>> > "user_buf->length" is in user space, and copied in twice. The second
>> > copy is after it passes the security check. If a user program races to
>> > change user_buf->length in user space, the data fetched in the second
>> > copy may invalidate the security check. The fix avoids the double-fetch
>> > issue by using the value passing the security check.
>>
>> AFAICS the patch really does two things: it avoids the issue described
>> above and avoids using the (redundant) 'table' local variable on the
>> stack. Arguably, you could fix the issue without getting rid of the
>> redundant variable.
>>
>> >
>> > Signed-off-by: Kangjie Lu <kjlu@umn.edu>
>> > ---
>> > drivers/acpi/custom_method.c | 10 ++++++----
>> > 1 file changed, 6 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
>> > index 4451877f83b6..f10ee0519033 100644
>> > --- a/drivers/acpi/custom_method.c
>> > +++ b/drivers/acpi/custom_method.c
>> > @@ -26,17 +26,16 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
>> > static u32 max_size;
>> > static u32 uncopied_bytes;
>> >
>> > - struct acpi_table_header table;
>> > acpi_status status;
>> >
>> > if (!(*ppos)) {
>> > /* parse the table header to get the table length */
>> > if (count <= sizeof(struct acpi_table_header))
>> > return -EINVAL;
>> > - if (copy_from_user(&table, user_buf,
>> > - sizeof(struct acpi_table_header)))
>> > + if (get_user(max_size,
>> > + &((struct acpi_table_header *)user_buf)->length))
>> > return -EFAULT;
>> > - uncopied_bytes = max_size = table.length;
>> > + uncopied_bytes = max_size;
>> > buf = kzalloc(max_size, GFP_KERNEL);
>> > if (!buf)
>> > return -ENOMEM;
>> > @@ -57,6 +56,9 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
>> > return -EFAULT;
>> > }
>> >
>> > + /* Ensure table length is not changed in the second copy */
>> > + ((struct acpi_table_header *)(buf + (*ppos)))->length = max_size;
>>
>> Why don't you return -EFAULT if max_size is different from ->length?
>> Surely, the table should not be used at all in that case.
>
>
> We could do either, but I didn't see one is clearly better than the other.
As I said, why would you use any inconsistent data instead of
returning an error?
>>
>> Moreover, wouldn't it be even better to compare the entire header with
>> the one read previously and return -EFAULT if they don't match?
>
>
> If other fields are not critical and thus not checked, we don't have to compare
> the entire header for better performance reasons.
If you really care about consistency, performance doesn't matter that much.
Thanks,
Rafael
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-01-15 19:05 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-12-25 21:46 [PATCH] acpi: fix a potential inconsistency caused by double-fetch Kangjie Lu
2018-12-25 22:20 ` kbuild test robot
2018-12-26 0:11 ` kbuild test robot
2019-01-09 8:14 ` [PATCH v2] " Kangjie Lu
2019-01-14 11:15 ` Rafael J. Wysocki
[not found] ` <CAK8KejpGipqLpR93=ZnRze9FU7q5ZhJrGQV33czZwuxqSs0AyQ@mail.gmail.com>
2019-01-15 19:05 ` Rafael J. Wysocki
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