Hello Dmitry Monakhov,
The patch fdfe07398761: "ext4: fix potential use after free during
resize" from Dec 2, 2014, leads to the following static checker
warning:
fs/ext4/balloc.c:300 ext4_get_group_desc()
warn: 'gd_bh' can't be NULL.
This is a false positive in Smatch, but I still had a question about the
code.
fs/ext4/balloc.c
295 group_desc = block_group >> EXT4_DESC_PER_BLOCK_BITS(sb);
296 offset = block_group & (EXT4_DESC_PER_BLOCK(sb) - 1);
297 rcu_read_lock();
298 gd_bh = *rcu_dereference(sbi->s_group_desc) + group_desc;
299 rcu_read_unlock();
300 if (!gd_bh) {
Are you sure you don't want to "*rcu_dereference(sbi->s_group_desc)"
separate from group_desc?
gd_bh = *rcu_dereference(sbi->s_group_desc);
rcu_read_unlock();
if (!gd_bh) {
...
}
gd_bh = (u8 *) + group_desc;
301 ext4_error(sb, "Group descriptor not loaded - "
302 "block_group = %u, group_desc = %u, desc = %u",
303 block_group, group_desc, offset);
^^^^^^^^^^
We already know this is zero.
304 return NULL;
305 }
306
307 desc = (struct ext4_group_desc *)(
308 (__u8 *)gd_bh->b_data + offset * EXT4_DESC_SIZE(sb));
309 if (bh)
310 *bh = gd_bh;
regards,
dan carpenter
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