m68k: bitops - Never step beyond the end of the bitmap

find_next bitops on m68k (find_next_zero_bit, find_next_bit, and
find_next_bit_le) may cause out of bounds memory access
when the bitmap size in bits % 32 != 0 and offset (the bitnumber
to start searching at) is very close to the bitmap size.

For example,

       unsigned long bitmap[2] = { 0, 0 };
       find_next_bit(bitmap, 63, 62);

1. find_next_bit() tries to find any set bits in bitmap[1],
   but no bits set.

2. Then find_first_bit(bimap + 2, -1)

3. Unfortunately find_first_bit() takes unsigned int as the size argument.

4. find_first_bit will access bitmap[2~] until it find any set bits.

Add missing tests for stepping beyond the end of the bitmap to all
find_{first,next}_*() functions, and make sure they never return a value
larger than the bitmap size.

Reported-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

1 files changed, 55 insertions, 26 deletions

diff --git a/arch/m68k/include/asm/bitops_mm.h b/arch/m68k/include/asm/bitops_mm.h
index 5bd3afadeafa..e9020f88a748 100644
--- a/arch/m68k/include/asm/bitops_mm.h
+++ b/arch/m68k/include/asm/bitops_mm.h
@@ -181,14 +181,15 @@ static inline int find_first_zero_bit(const unsigned long *vaddr,
 {
         const unsigned long *p = vaddr;
         int res = 32;
+        unsigned int words;
         unsigned long num;
 
         if (!size)
                 return 0;
 
-        size = (size + 31) >> 5;
+        words = (size + 31) >> 5;
         while (!(num = ~*p++)) {
-                if (!--size)
+                if (!--words)
                         goto out;
         }
 
@@ -196,7 +197,8 @@ static inline int find_first_zero_bit(const unsigned long *vaddr,
                               : "=d" (res) : "d" (num & -num));
         res ^= 31;
 out:
-        return ((long)p - (long)vaddr - 4) * 8 + res;
+        res += ((long)p - (long)vaddr - 4) * 8;
+        return res < size ? res : size;
 }
 
 static inline int find_next_zero_bit(const unsigned long *vaddr, int size,
@@ -215,9 +217,14 @@ static inline int find_next_zero_bit(const unsigned long *vaddr, int size,
                 /* Look for zero in first longword */
                 __asm__ __volatile__ ("bfffo %1{#0,#0},%0"
                                       : "=d" (res) : "d" (num & -num));
-                if (res < 32)
-                        return offset + (res ^ 31);
+                if (res < 32) {
+                        offset += res ^ 31;
+                        return offset < size ? offset : size;
+                }
                 offset += 32;
+
+                if (offset >= size)
+                        return size;
         }
         /* No zero yet, search remaining full bytes for a zero */
         return offset + find_first_zero_bit(p, size - offset);
@@ -227,14 +234,15 @@ static inline int find_first_bit(const unsigned long *vaddr, unsigned size)
 {
         const unsigned long *p = vaddr;
         int res = 32;
+        unsigned int words;
         unsigned long num;
 
         if (!size)
                 return 0;
 
-        size = (size + 31) >> 5;
+        words = (size + 31) >> 5;
         while (!(num = *p++)) {
-                if (!--size)
+                if (!--words)
                         goto out;
         }
 
@@ -242,7 +250,8 @@ static inline int find_first_bit(const unsigned long *vaddr, unsigned size)
                               : "=d" (res) : "d" (num & -num));
         res ^= 31;
 out:
-        return ((long)p - (long)vaddr - 4) * 8 + res;
+        res += ((long)p - (long)vaddr - 4) * 8;
+        return res < size ? res : size;
 }
 
 static inline int find_next_bit(const unsigned long *vaddr, int size,
@@ -261,9 +270,14 @@ static inline int find_next_bit(const unsigned long *vaddr, int size,
                 /* Look for one in first longword */
                 __asm__ __volatile__ ("bfffo %1{#0,#0},%0"
                                       : "=d" (res) : "d" (num & -num));
-                if (res < 32)
-                        return offset + (res ^ 31);
+                if (res < 32) {
+                        offset += res ^ 31;
+                        return offset < size ? offset : size;
+                }
                 offset += 32;
+
+                if (offset >= size)
+                        return size;
         }
         /* No one yet, search remaining full bytes for a one */
         return offset + find_first_bit(p, size - offset);
@@ -364,23 +378,25 @@ static inline int test_bit_le(int nr, const void *vaddr)
 static inline int find_first_zero_bit_le(const void *vaddr, unsigned size)
 {
         const unsigned long *p = vaddr, *addr = vaddr;
-        int res;
+        int res = 0;
+        unsigned int words;
 
         if (!size)
                 return 0;
 
-        size = (size >> 5) + ((size & 31) > 0);
-        while (*p++ == ~0UL)
-        {
-                if (--size == 0)
-                        return (p - addr) << 5;
+        words = (size >> 5) + ((size & 31) > 0);
+        while (*p++ == ~0UL) {
+                if (--words == 0)
+                        goto out;
         }
 
         --p;
         for (res = 0; res < 32; res++)
                 if (!test_bit_le(res, p))
                         break;
-        return (p - addr) * 32 + res;
+out:
+        res += (p - addr) * 32;
+        return res < size ? res : size;
 }
 
 static inline unsigned long find_next_zero_bit_le(const void *addr,
@@ -398,10 +414,15 @@ static inline unsigned long find_next_zero_bit_le(const void *addr,
                 offset -= bit;
                 /* Look for zero in first longword */
                 for (res = bit; res < 32; res++)
-                        if (!test_bit_le(res, p))
-                                return offset + res;
+                        if (!test_bit_le(res, p)) {
+                                offset += res;
+                                return offset < size ? offset : size;
+                        }
                 p++;
                 offset += 32;
+
+                if (offset >= size)
+                        return size;
         }
         /* No zero yet, search remaining full bytes for a zero */
         return offset + find_first_zero_bit_le(p, size - offset);
@@ -410,22 +431,25 @@ static inline unsigned long find_next_zero_bit_le(const void *addr,
 static inline int find_first_bit_le(const void *vaddr, unsigned size)
 {
         const unsigned long *p = vaddr, *addr = vaddr;
-        int res;
+        int res = 0;
+        unsigned int words;
 
         if (!size)
                 return 0;
 
-        size = (size >> 5) + ((size & 31) > 0);
+        words = (size >> 5) + ((size & 31) > 0);
         while (*p++ == 0UL) {
-                if (--size == 0)
-                        return (p - addr) << 5;
+                if (--words == 0)
+                        goto out;
         }
 
         --p;
         for (res = 0; res < 32; res++)
                 if (test_bit_le(res, p))
                         break;
-        return (p - addr) * 32 + res;
+out:
+        res += (p - addr) * 32;
+        return res < size ? res : size;
 }
 
 static inline unsigned long find_next_bit_le(const void *addr,
@@ -443,10 +467,15 @@ static inline unsigned long find_next_bit_le(const void *addr,
                 offset -= bit;
                 /* Look for one in first longword */
                 for (res = bit; res < 32; res++)
-                        if (test_bit_le(res, p))
-                                return offset + res;
+                        if (test_bit_le(res, p)) {
+                                offset += res;
+                                return offset < size ? offset : size;
+                        }
                 p++;
                 offset += 32;
+
+                if (offset >= size)
+                        return size;
         }
         /* No set bit yet, search remaining full bytes for a set bit */
         return offset + find_first_bit_le(p, size - offset);