bcache: improve sysfs_strtoul_clamp()

BugLink: https://bugs.launchpad.net/bugs/1838116
[ Upstream commit 596b5a5dd1bc2fa019fdaaae522ef331deef927f ]

Currently sysfs_strtoul_clamp() is defined as,
 82 #define sysfs_strtoul_clamp(file, var, min, max)                   \
 83 do {                                                               \
 84         if (attr == &sysfs_ ## file)                               \
 85                 return strtoul_safe_clamp(buf, var, min, max)      \
 86                         ?: (ssize_t) size;                         \
 87 } while (0)

The problem is, if bit width of var is less then unsigned long, min and
max may not protect var from integer overflow, because overflow happens
in strtoul_safe_clamp() before checking min and max.

To fix such overflow in sysfs_strtoul_clamp(), to make min and max take
effect, this patch adds an unsigned long variable, and uses it to macro
strtoul_safe_clamp() to convert an unsigned long value in range defined
by [min, max]. Then assign this value to var. By this method, if bit
width of var is less than unsigned long, integer overflow won't happen
before min and max are checking.

Now sysfs_strtoul_clamp() can properly handle smaller data type like
unsigned int, of cause min and max should be defined in range of
unsigned int too.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/md/bcache/sysfs.h b/drivers/md/bcache/sysfs.h
index b54fe9602529ebda4ab71e7d306617137290cf39..e6e258f897ca7f2acc8fea54d1b71fd64b0fb06d 100644 (file)
--- a/drivers/md/bcache/sysfs.h
+++ b/drivers/md/bcache/sysfs.h
@@ -81,9 +81,16 @@ do {                                                                 \
 
 #define sysfs_strtoul_clamp(file, var, min, max)                       \
 do {                                                                   \
-       if (attr == &sysfs_ ## file)                                    \
-               return strtoul_safe_clamp(buf, var, min, max)           \
-                       ?: (ssize_t) size;                              \
+       if (attr == &sysfs_ ## file) {                                  \
+               unsigned long v = 0;                                    \
+               ssize_t ret;                                            \
+               ret = strtoul_safe_clamp(buf, v, min, max);             \
+               if (!ret) {                                             \
+                       var = v;                                        \
+                       return size;                                    \
+               }                                                       \
+               return ret;                                             \
+       }                                                               \
 } while (0)
 
 #define strtoul_or_return(cp)                                          \