From 8c97a6ddc95690a938ded44b4e3202f03f15078c Mon Sep 17 00:00:00 2001 From: Jori Koolstra Date: Mon, 8 Dec 2025 16:39:47 +0100 Subject: [PATCH] minix: Add required sanity checking to minix_check_superblock() 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 Link: https://patch.msgid.link/20251208153947.108343-1-jkoolstra@xs4all.nl Reviewed-by: Jan Kara Reported-by: syzbot+5ad0824204c7bf9b67f2@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=5ad0824204c7bf9b67f2 Signed-off-by: Christian Brauner --- 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 51ea9bdc813f7..c8c6b2135abe7 100644 --- a/fs/minix/inode.c +++ b/fs/minix/inode.c @@ -170,10 +170,38 @@ 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 @@ -293,26 +321,6 @@ 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; -- 2.47.3