btrfs: fix race between quota disable and quota assign ioctls

[platform/kernel/linux-rpi.git] / lib / hexdump.c

diff --git a/lib/hexdump.c b/lib/hexdump.c
index 9301578..06833d4 100644 (file)
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -22,15 +22,33 @@ EXPORT_SYMBOL(hex_asc_upper);
  *
  * hex_to_bin() converts one hex digit to its actual value or -1 in case of bad
  * input.
+ *
+ * This function is used to load cryptographic keys, so it is coded in such a
+ * way that there are no conditions or memory accesses that depend on data.
+ *
+ * Explanation of the logic:
+ * (ch - '9' - 1) is negative if ch <= '9'
+ * ('0' - 1 - ch) is negative if ch >= '0'
+ * we "and" these two values, so the result is negative if ch is in the range
+ *     '0' ... '9'
+ * we are only interested in the sign, so we do a shift ">> 8"; note that right
+ *     shift of a negative value is implementation-defined, so we cast the
+ *     value to (unsigned) before the shift --- we have 0xffffff if ch is in
+ *     the range '0' ... '9', 0 otherwise
+ * we "and" this value with (ch - '0' + 1) --- we have a value 1 ... 10 if ch is
+ *     in the range '0' ... '9', 0 otherwise
+ * we add this value to -1 --- we have a value 0 ... 9 if ch is in the range '0'
+ *     ... '9', -1 otherwise
+ * the next line is similar to the previous one, but we need to decode both
+ *     uppercase and lowercase letters, so we use (ch & 0xdf), which converts
+ *     lowercase to uppercase
  */
-int hex_to_bin(char ch)
+int hex_to_bin(unsigned char ch)
 {
-       if ((ch >= '0') && (ch <= '9'))
-               return ch - '0';
-       ch = tolower(ch);
-       if ((ch >= 'a') && (ch <= 'f'))
-               return ch - 'a' + 10;
-       return -1;
+       unsigned char cu = ch & 0xdf;
+       return -1 +
+               ((ch - '0' +  1) & (unsigned)((ch - '9' - 1) & ('0' - 1 - ch)) >> 8) +
+               ((cu - 'A' + 11) & (unsigned)((cu - 'F' - 1) & ('A' - 1 - cu)) >> 8);
 }
 EXPORT_SYMBOL(hex_to_bin);
 
@@ -45,10 +63,13 @@ EXPORT_SYMBOL(hex_to_bin);
 int hex2bin(u8 *dst, const char *src, size_t count)
 {
        while (count--) {
-               int hi = hex_to_bin(*src++);
-               int lo = hex_to_bin(*src++);
+               int hi, lo;
 
-               if ((hi < 0) || (lo < 0))
+               hi = hex_to_bin(*src++);
+               if (unlikely(hi < 0))
+                       return -EINVAL;
+               lo = hex_to_bin(*src++);
+               if (unlikely(lo < 0))
                        return -EINVAL;
 
                *dst++ = (hi << 4) | lo;