From: Namjae Jeon <linkinjeon@kernel.org>
Date: Tue, 18 Nov 2025 02:10:26 +0000 (+0900)
Subject: exfat: fix divide-by-zero in exfat_allocate_bitmap
X-Git-Tag: v6.19-rc1~109^2~1
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d70a5804c563b5e34825353ba9927509df709651;p=thirdparty%2Fkernel%2Flinux.git

exfat: fix divide-by-zero in exfat_allocate_bitmap

The variable max_ra_count can be 0 in exfat_allocate_bitmap(),
which causes a divide-by-zero error in the subsequent modulo operation
(i % max_ra_count), leading to a system crash.
When max_ra_count is 0, it means that readahead is not used. This patch
load the bitmap without readahead.

Fixes: 9fd688678dd8 ("exfat: optimize allocation bitmap loading time")
Reported-by: Jiaming Zhang <r772577952@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
---

diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
index b387bf7df65e8..5429041c7eaf9 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);