On 03/03, Colin Ian King wrote:
> On 03/03/2021 19:44, Jaegeuk Kim wrote:
> > On 03/02, Colin Ian King wrote:
> >> Hi,
> >>
> >> Static analysis on linux-next detected a potential uninitialized
> >> variable dn.node_changed that does not get set when a call to
> >> f2fs_get_node_page() fails. This uninitialized value gets used in the
> >> call to f2fs_balance_fs() that may or not may not balances dirty node
> >> and dentry pages depending on the uninitialized state of the variable.
> >>
> >> I believe the issue was introduced by commit:
> >>
> >> commit 2a3407607028f7c780f1c20faa4e922bf631d340
> >> Author: Jaegeuk Kim <jaeg...@kernel.org>
> >> Date: Tue Dec 22 13:23:35 2015 -0800
> >>
> >> f2fs: call f2fs_balance_fs only when node was changed
> >>
> >>
> >> The analysis is a follows:
> >>
> >> 184 int f2fs_convert_inline_inode(struct inode *inode)
> >> 185 {
> >> 186 struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >>
> >> 1. var_decl: Declaring variable dn without initializer.
> >>
> >> 187 struct dnode_of_data dn;
> >>
> >> NOTE dn is not initialized here.
> >>
> >> 188 struct page *ipage, *page;
> >> 189 int err = 0;
> >> 190
> >>
> >> 2. Condition !f2fs_has_inline_data(inode), taking false branch.
> >> 3. Condition f2fs_hw_is_readonly(sbi), taking false branch.
> >> 4. Condition f2fs_readonly(sbi->sb), taking false branch.
> >>
> >> 191 if (!f2fs_has_inline_data(inode) ||
> >> 192 f2fs_hw_is_readonly(sbi) ||
> >> f2fs_readonly(sbi->sb))
> >> 193 return 0;
> >> 194
> >> 195 err = dquot_initialize(inode);
> >>
> >> 5. Condition err, taking false branch.
> >>
> >> 196 if (err)
> >> 197 return err;
> >> 198
> >> 199 page = f2fs_grab_cache_page(inode->i_mapping, 0, false);
> >>
> >> 6. Condition !page, taking false branch.
> >>
> >> 200 if (!page)
> >> 201 return -ENOMEM;
> >> 202
> >> 203 f2fs_lock_op(sbi);
> >> 204
> >> 205 ipage = f2fs_get_node_page(sbi, inode->i_ino);
> >>
> >> 7. Condition IS_ERR(ipage), taking true branch.
> >>
> >> 206 if (IS_ERR(ipage)) {
> >> 207 err = PTR_ERR(ipage);
> >>
> >> 8. Jumping to label out.
> >>
> >> 208 goto out;
> >> 209 }
> >> 210
> >>
> >> NOTE: set_new_dnode memset's dn so sets the flag to false, but we
> >> don't get to this memset if IS_ERR(ipage) above is true.
> >>
> >> 211 set_new_dnode(&dn, inode, ipage, ipage, 0);
> >> 212
> >> 213 if (f2fs_has_inline_data(inode))
> >> 214 err = f2fs_convert_inline_page(&dn, page);
> >> 215
> >> 216 f2fs_put_dnode(&dn);
> >> 217 out:
> >> 218 f2fs_unlock_op(sbi);
> >> 219
> >> 220 f2fs_put_page(page, 1);
> >> 221
> >>
> >> Uninitialized scalar variable:
> >>
> >> 9. uninit_use_in_call: Using uninitialized value dn.node_changed when
> >> calling f2fs_balance_fs.
> >>
> >> 222 f2fs_balance_fs(sbi, dn.node_changed);
> >> 223
> >> 224 return err;
> >> 225 }
> >>
> >> I think a suitable fix will be to set dn.node_changed to false on in
> >> line 207-208 but I'm concerned if I'm missing something subtle to the
> >> rebalancing if I do this.
> >>
> >> Comments?
> >
> > Thank you for the report. Yes, it seems that's a right call and we need to
> > check the error to decide calling f2fs_balance_fs() in line 222, since
> > set_new_dnode() is used to set all the fields in dnode_of_data. So, if you
> > don't mind, could you please post a patch?
>
> Just to clarify, just setting dn.node_changes to false is enough?
>
> I'm not entirely sure what you meant when you wrote "and we need to
> check the error to decide calling f2fs_balance_fs() in line 222".
I meant:
222 if (!err)
223 f2fs_balance_fs(sbi, dn.node_changed);
Thanks,
>
> Colin
>
> >
> > Thanks,
> >
> >>
> >> Colin
> >>
