[PATCH v2 3/3] fs: ext4: widen ext4fs_update() block-group loop counter

[Sriram Sriram <sriramsriram@linux.microsoft.com>]

From: Daniel Munic <v-dmunic@microsoft.com>

ext4fs_update() iterates over all block groups with a signed 16-bit
loop counter:

	short i;
	...
	for (i = 0; i < fs->no_blkgrp; i++)

fs->no_blkgrp is a uint32_t. On a filesystem with more than 32767
block groups the counter cannot represent every index: incrementing
past SHRT_MAX is signed overflow (undefined behaviour) and the
comparison against the unsigned no_blkgrp never terminates correctly,
so the bitmap/group-descriptor write-back loops misbehave. The mixed
signed/unsigned comparison is also flagged by static analysis.

Use u32 for the loop counter, matching the width of no_blkgrp.

Signed-off-by: Daniel Munic <v-dmunic@microsoft.com>
Signed-off-by: Sriram Sriram <sriramsriram@linux.microsoft.com>
---
Changes in v2:
 - No change, rebased onto current master.

 fs/ext4/ext4_write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/ext4_write.c b/fs/ext4/ext4_write.c
index 1abedcede72..2fba2197c19 100644
--- a/fs/ext4/ext4_write.c
+++ b/fs/ext4/ext4_write.c
@@ -67,7 +67,7 @@ static inline void ext4fs_bg_free_blocks_inc
 
 static void ext4fs_update(void)
 {
-	short i;
+	u32 i;
 	ext4fs_update_journal();
 	struct ext_filesystem *fs = get_fs();
 	struct ext2_block_group *bgd = NULL;
-- 
2.49.0