[bug report] fs/ntfs3: inconsistent NULL checks in mi_read()

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Konstantin Komarov,

The patch 4342306f0f0d: "fs/ntfs3: Add file operations and
implementation" from Aug 13, 2021, leads to the following
Smatch static checker warning:

	fs/ntfs3/record.c:158 mi_read()
	warn: potential NULL parameter dereference 'mft_ni'

fs/ntfs3/record.c
    122 int mi_read(struct mft_inode *mi, bool is_mft)
    123 {
    124 	int err;
    125 	struct MFT_REC *rec = mi->mrec;
    126 	struct ntfs_sb_info *sbi = mi->sbi;
    127 	u32 bpr = sbi->record_size;
    128 	u64 vbo = (u64)mi->rno << sbi->record_bits;
    129 	struct ntfs_inode *mft_ni = sbi->mft.ni;
    130 	struct runs_tree *run = mft_ni ? &mft_ni->file.run : NULL;
                                        ^^^^^^
Can mft_ni be NULL?

    131 	struct rw_semaphore *rw_lock = NULL;
    132 
    133 	if (is_mounted(sbi)) {
    134 		if (!is_mft) {
    135 			rw_lock = &mft_ni->file.run_lock;
    136 			down_read(rw_lock);
    137 		}
    138 	}
    139 
    140 	err = ntfs_read_bh(sbi, run, vbo, &rec->rhdr, bpr, &mi->nb);
    141 	if (rw_lock)
    142 		up_read(rw_lock);
    143 	if (!err)
    144 		goto ok;
    145 
    146 	if (err == -E_NTFS_FIXUP) {
    147 		mi->dirty = true;
    148 		goto ok;
    149 	}
    150 
    151 	if (err != -ENOENT)
    152 		goto out;
    153 
    154 	if (rw_lock) {
    155 		ni_lock(mft_ni);
    156 		down_write(rw_lock);
    157 	}
--> 158 	err = attr_load_runs_vcn(mft_ni, ATTR_DATA, NULL, 0, &mft_ni->file.run,
                                         ^^^^^^
Unchecked dereference inside the function.

    159 				 vbo >> sbi->cluster_bits);
    160 	if (rw_lock) {
    161 		up_write(rw_lock);
    162 		ni_unlock(mft_ni);
    163 	}
    164 	if (err)
    165 		goto out;
    166 
    167 	if (rw_lock)
    168 		down_read(rw_lock);
    169 	err = ntfs_read_bh(sbi, run, vbo, &rec->rhdr, bpr, &mi->nb);
    170 	if (rw_lock)
    171 		up_read(rw_lock);
    172 
    173 	if (err == -E_NTFS_FIXUP) {
    174 		mi->dirty = true;
    175 		goto ok;
    176 	}
    177 	if (err)
    178 		goto out;
    179 
    180 ok:
    181 	/* check field 'total' only here */
    182 	if (le32_to_cpu(rec->total) != bpr) {
    183 		err = -EINVAL;
    184 		goto out;
    185 	}
    186 
    187 	return 0;
    188 
    189 out:
    190 	return err;
    191 }

regards,
dan carpenter