[PATCH] nilfs2: fix possible int overflows in nilfs_fiemap()

[Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>]

Since nilfs_bmap_lookup_contig() in nilfs_fiemap() calculates its
result by being prepared to go through potentially
maxblocks == INT_MAX blocks, the value in n may experience an
overflow caused by left shift of blkbits.

While it is extremely unlikely to occur, play it safe and cast right
hand expression to wider type to mitigate the issue.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: 622daaff0a89 ("nilfs2: fiemap support")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>
---
 fs/nilfs2/inode.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 23f3a75edd50..81abb58dcbd8 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -1188,7 +1188,7 @@ int nilfs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 			if (size) {
 				if (phys && blkphy << blkbits == phys + size) {
 					/* The current extent goes on */
-					size += n << blkbits;
+					size += (u64)n << blkbits;
 				} else {
 					/* Terminate the current extent */
 					ret = fiemap_fill_next_extent(
@@ -1201,14 +1201,14 @@ int nilfs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 					flags = FIEMAP_EXTENT_MERGED;
 					logical = blkoff << blkbits;
 					phys = blkphy << blkbits;
-					size = n << blkbits;
+					size = (u64)n << blkbits;
 				}
 			} else {
 				/* Start a new extent */
 				flags = FIEMAP_EXTENT_MERGED;
 				logical = blkoff << blkbits;
 				phys = blkphy << blkbits;
-				size = n << blkbits;
+				size = (u64)n << blkbits;
 			}
 			blkoff += n;
 		}