[07/19] bcache: improve sysfs_strtoul_clamp()
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Message ID 20190209045311.15677-8-colyli@suse.de
State New
Headers show
Series
  • bcache patches for Linux v5.1
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Commit Message

Coly Li Feb. 9, 2019, 4:52 a.m. UTC
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>
---
 drivers/md/bcache/sysfs.h | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

Patch
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diff --git a/drivers/md/bcache/sysfs.h b/drivers/md/bcache/sysfs.h
index 3fe82425859c..0ad2715a884e 100644
--- 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)						\