[PATCH 6.18 034/752] minix: Add required sanity checking to minix_check_superblock()

Sasha Levin
2026-02-28T17:48:38Z

From: Jori Koolstra <jkoolstra@xs4all.nl>

[ Upstream commit 8c97a6ddc95690a938ded44b4e3202f03f15078c ]

The fs/minix implementation of the minix filesystem does not currently
support any other value for s_log_zone_size than 0. This is also the
only value supported in util-linux; see mkfs.minix.c line 511. In
addition, this patch adds some sanity checking for the other minix
superblock fields, and moves the minix_blocks_needed() checks for the
zmap and imap also to minix_check_super_block().

This also closes a related syzbot bug report.

Signed-off-by: Jori Koolstra <jkoolstra@xs4all.nl>
Link: https://patch.msgid.link/20251208153947.108343-1-jkoolstra@xs4all.nl
Reviewed-by: Jan Kara <jack@suse.cz>
Reported-by: syzbot+5ad0824204c7bf9b67f2@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5ad0824204c7bf9b67f2
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/minix/inode.c | 50 ++++++++++++++++++++++++++++--------------------
1 file changed, 29 insertions(+), 21 deletions(-)

diff --git a/fs/minix/inode.c b/fs/minix/inode.c
index 32db676127a9e..7bdd240ea1584 100644
--- a/fs/minix/inode.c
+++ b/fs/minix/inode.c
@@ -154,10 +154,38 @@ static int minix_reconfigure(struct fs_context *fc)
static bool minix_check_superblock(struct super_block *sb)
{
struct minix_sb_info *sbi = minix_sb(sb);
+ unsigned long block;

- if (sbi->s_imap_blocks == 0 || sbi->s_zmap_blocks == 0)
+ if (sbi->s_log_zone_size != 0) {
+ printk("minix-fs error: zone size must equal block size. "
+ "s_log_zone_size > 0 is not supported.\n");
+ return false;
+ }
+
+ if (sbi->s_ninodes < 1 || sbi->s_firstdatazone <= 4 ||
+ sbi->s_firstdatazone >= sbi->s_nzones)
return false;

+ /* Apparently minix can create filesystems that allocate more blocks for
+ * the bitmaps than needed. We simply ignore that, but verify it didn't
+ * create one with not enough blocks and bail out if so.
+ */
+ block = minix_blocks_needed(sbi->s_ninodes, sb->s_blocksize);
+ if (sbi->s_imap_blocks < block) {
+ printk("MINIX-fs: file system does not have enough "
+ "imap blocks allocated. Refusing to mount.\n");
+ return false;
+ }
+
+ block = minix_blocks_needed(
+ (sbi->s_nzones - sbi->s_firstdatazone + 1),
+ sb->s_blocksize);
+ if (sbi->s_zmap_blocks < block) {
+ printk("MINIX-fs: file system does not have enough "
+ "zmap blocks allocated. Refusing to mount.\n");
+ return false;
+ }
+
/*
* s_max_size must not exceed the block mapping limitation. This check
* is only needed for V1 filesystems, since V2/V3 support an extra level
@@ -277,26 +305,6 @@ static int minix_fill_super(struct super_block *s, struct fs_context *fc)
minix_set_bit(0,sbi->s_imap[0]->b_data);
minix_set_bit(0,sbi->s_zmap[0]->b_data);

- /* Apparently minix can create filesystems that allocate more blocks for
- * the bitmaps than needed. We simply ignore that, but verify it didn't
- * create one with not enough blocks and bail out if so.
- */
- block = minix_blocks_needed(sbi->s_ninodes, s->s_blocksize);
- if (sbi->s_imap_blocks < block) {
- printk("MINIX-fs: file system does not have enough "
- "imap blocks allocated. Refusing to mount.\n");
- goto out_no_bitmap;
- }
-
- block = minix_blocks_needed(
- (sbi->s_nzones - sbi->s_firstdatazone + 1),
- s->s_blocksize);
- if (sbi->s_zmap_blocks < block) {
- printk("MINIX-fs: file system does not have enough "
- "zmap blocks allocated. Refusing to mount.\n");
- goto out_no_bitmap;
- }
-
/* set up enough so that it can read an inode */
s->s_op = &minix_sops;
s->s_time_min = 0;
--
2.51.0