Re: [PATCH] acpi: fix a potential inconsistency caused by double-fetch

[kbuild test robot <lkp@intel.com>]

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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	

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