Entreprise française de cybersécurité depuis 2004
☎ 03 60 47 09 81 - info@securiteinfo.com
☎ 03 60 47 09 81 - info@securiteinfo.com
In the Linux kernel, the following vulnerability has been resolved:ext4: avoid journaling sb update on error if journal is destroyingPresently we always BUG_ON if trying to start a transaction on a journal markedwith JBD2_UNMOUNT, since this should never happen. However, while ltp runningstress tests, it was observed that in case of some error handling paths, it ispossible for update_super_work to start a transaction after the journal isdestroyed eg:(umount)ext4_kill_sb kill_block_super generic_shutdown_super sync_filesystem /* commits all txns */ evict_inodes /* might start a new txn */ ext4_put_super flush_work(&sbi->s_sb_upd_work) /* flush the workqueue */ jbd2_journal_destroy journal_kill_thread journal->j_flags |= JBD2_UNMOUNT; jbd2_journal_commit_transaction jbd2_journal_get_descriptor_buffer jbd2_journal_bmap ext4_journal_bmap ext4_map_blocks ... ext4_inode_error ext4_handle_error schedule_work(&sbi->s_sb_upd_work) /* work queue kicks in */ update_super_work jbd2_journal_start start_this_handle BUG_ON(journal->j_flags & JBD2_UNMOUNT)Hence, introduce a new mount flag to indicate journal is destroying and only doa journaled (and deferred) update of sb if this flag is not set. Otherwise, justfallback to an un-journaled commit.Further, in the journal destroy path, we have the following sequence: 1. Set mount flag indicating journal is destroying 2. force a commit and wait for it 3. flush pending sb updatesThis sequence is important as it ensures that, after this point, there is no sbupdate that might be journaled so it is safe to update the sb outside thejournal. (To avoid race discussed in 2d01ddc86606)Also, we don't need a similar check in ext4_grp_locked_error since it is onlycalled from mballoc and AFAICT it would be always valid to schedule work here.
No PoCs from references.
- https://github.com/w4zu/Debian_security