From: HyungJung Joo Date: Tue, 17 Mar 2026 05:48:27 +0000 (+0900) Subject: fs/omfs: reject s_sys_blocksize smaller than OMFS_DIR_START X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=0621c385fda1376e967f37ccd534c26c3e511d14;p=thirdparty%2Fkernel%2Flinux.git fs/omfs: reject s_sys_blocksize smaller than OMFS_DIR_START omfs_fill_super() rejects oversized s_sys_blocksize values (> PAGE_SIZE), but it does not reject values smaller than OMFS_DIR_START (0x1b8 = 440). Later, omfs_make_empty() uses sbi->s_sys_blocksize - OMFS_DIR_START as the length argument to memset(). Since s_sys_blocksize is u32, a crafted filesystem image with s_sys_blocksize < OMFS_DIR_START causes an unsigned underflow there, wrapping to a value near 2^32. That drives a ~4 GiB memset() from bh->b_data + OMFS_DIR_START and overwrites kernel memory far beyond the backing block buffer. Add the corresponding lower-bound check alongside the existing upper-bound check in omfs_fill_super(), so that malformed images are rejected during superblock validation before any filesystem data is processed. Fixes: a3ab7155ea21 ("omfs: add directory routines") Signed-off-by: Hyungjung Joo Link: https://patch.msgid.link/20260317054827.1822061-1-jhj140711@gmail.com Signed-off-by: Christian Brauner --- diff --git a/fs/omfs/inode.c b/fs/omfs/inode.c index 701ed85d9831..23aa3f54aaba 100644 --- a/fs/omfs/inode.c +++ b/fs/omfs/inode.c @@ -513,6 +513,12 @@ static int omfs_fill_super(struct super_block *sb, struct fs_context *fc) goto out_brelse_bh; } + if (sbi->s_sys_blocksize < OMFS_DIR_START) { + printk(KERN_ERR "omfs: sysblock size (%d) is too small\n", + sbi->s_sys_blocksize); + goto out_brelse_bh; + } + if (sbi->s_blocksize < sbi->s_sys_blocksize || sbi->s_blocksize > OMFS_MAX_BLOCK_SIZE) { printk(KERN_ERR "omfs: block size (%d) is out of range\n",