linux-kernel - [PATCH 1/1] exfat: fix divide error in exfat_allocate

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Message-Id: <20251118073338.576334-2-r772577952@gmail.com>
Date: Tue, 18 Nov 2025 15:33:38 +0800
From: Jiaming Zhang <r772577952@...il.com>
To: linkinjeon@...nel.org
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	r772577952@...il.com,
	sj1557.seo@...sung.com,
	syzkaller@...glegroups.com,
	yuezhang.mo@...y.com
Subject: [PATCH 1/1] exfat: fix divide error in exfat_allocate_bitmap()

The variable max_ra_count in exfat_allocate_bitmap() can be 0, leading
to a divide-by-zero error in the modulo operation (i % max_ra_count)
inside the loop. Avoid this by adding a check for max_ra_count before
performing the modulo operation.

Fixes: 9fd688678dd8
Closes: https://lore.kernel.org/lkml/CANypQFb0NeToJrTY5PQi57K_440xQJ1uUS2pMOKqLsqTdEGbRw@mail.gmail.com/
Suggested-by: Namjae Jeon <linkinjeon@...nel.org>
Signed-off-by: Jiaming Zhang <r772577952@...il.com>
---
 fs/exfat/balloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
index 2d2d510f2372..0b6466b3490a 100644
--- a/fs/exfat/balloc.c
+++ b/fs/exfat/balloc.c
@@ -106,7 +106,7 @@ static int exfat_allocate_bitmap(struct super_block *sb,
 		(PAGE_SHIFT - sb->s_blocksize_bits);
 	for (i = 0; i < sbi->map_sectors; i++) {
 		/* Trigger the next readahead in advance. */
-		if (0 == (i % max_ra_count)) {
+		if (max_ra_count && 0 == (i % max_ra_count)) {
 			blk_start_plug(&plug);
 			for (j = i; j < min(max_ra_count, sbi->map_sectors - i) + i; j++)
 				sb_breadahead(sb, sector + j);
-- 
2.34.1