[PATCH 5.19 0950/1157] lib/bitmap: fix off-by-one in bitmap_to_arr64()

[Greg Kroah-Hartman]

From: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>

[ Upstream commit 428bc098635680a664779f26f24fe9197d186172 ]

GENMASK*() family takes the first and the last bits of the mask
*including* them. So, with the current code bitmap_to_arr64()
doesn't clear the tail properly:

nbits %  exp             mask                must be
1        GENMASK(1, 0)   0x3                 0x1
...
63       GENMASK(63, 0)  0xffffffffffffffff  0x7fffffffffffffff

This was found by making the function always available instead of
32-bit BE systems only (for reusing in some new functionality).
Turn the number of bits into the last bit set by subtracting 1.
@nbits is already checked to be positive beforehand.

Fixes: 0a97953fd221 ("lib: add bitmap_{from,to}_arr64")
Signed-off-by: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 lib/bitmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index b18e31ea6e66..e903e13c62e1 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -1564,7 +1564,7 @@ void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits)
 
 	/* Clear tail bits in the last element of array beyond nbits. */
 	if (nbits % 64)
-		buf[-1] &= GENMASK_ULL(nbits % 64, 0);
+		buf[-1] &= GENMASK_ULL((nbits - 1) % 64, 0);
 }
 EXPORT_SYMBOL(bitmap_to_arr64);
 #endif
-- 
2.35.1