[PATCH 3.12 174/206] lib/bitmap.c: fix undefined shift in __bitmap_shift_{left|right}()

[Jiri Slaby]

From: Jan Kara <jack@xxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit ea5d05b34aca25c066e0699512d0ffbd8ee6ac3e upstream.

If __bitmap_shift_left() or __bitmap_shift_right() are asked to shift by
a multiple of BITS_PER_LONG, they will try to shift a long value by
BITS_PER_LONG bits which is undefined.  Change the functions to avoid
the undefined shift.

Coverity id: 1192175
Coverity id: 1192174
Signed-off-by: Jan Kara <jack@xxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 lib/bitmap.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 06f7e4fe8d2d..e5c4ebe586ba 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -131,7 +131,9 @@ void __bitmap_shift_right(unsigned long *dst,
 		lower = src[off + k];
 		if (left && off + k == lim - 1)
 			lower &= mask;
-		dst[k] = upper << (BITS_PER_LONG - rem) | lower >> rem;
+		dst[k] = lower >> rem;
+		if (rem)
+			dst[k] |= upper << (BITS_PER_LONG - rem);
 		if (left && k == lim - 1)
 			dst[k] &= mask;
 	}
@@ -172,7 +174,9 @@ void __bitmap_shift_left(unsigned long *dst,
 		upper = src[k];
 		if (left && k == lim - 1)
 			upper &= (1UL << left) - 1;
-		dst[k + off] = lower  >> (BITS_PER_LONG - rem) | upper << rem;
+		dst[k + off] = upper << rem;
+		if (rem)
+			dst[k + off] |= lower >> (BITS_PER_LONG - rem);
 		if (left && k + off == lim - 1)
 			dst[k + off] &= (1UL << left) - 1;
 	}
-- 
2.1.3

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