| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <YwFaTprvOf8ckGsP@google.com>
Date: Sat, 20 Aug 2022 15:03:58 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...nel.org>
Cc: Shuqi Zhang <zhangshuqi3@...wei.com>,
linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] f2fs: fix wrong dirty page count when race between
mmap and fallocate.
On 08/20, Chao Yu wrote:
> On 2022/8/15 16:15, Shuqi Zhang wrote:
> > This is a BUG_ON issue as follows when running xfstest-generic-503:
> > WARNING: CPU: 21 PID: 1385 at fs/f2fs/inode.c:762 f2fs_evict_inode+0x847/0xaa0
> > Modules linked in:
> > CPU: 21 PID: 1385 Comm: umount Not tainted 5.19.0-rc5+ #73
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014
> >
> > Call Trace:
> > evict+0x129/0x2d0
> > dispose_list+0x4f/0xb0
> > evict_inodes+0x204/0x230
> > generic_shutdown_super+0x5b/0x1e0
> > kill_block_super+0x29/0x80
> > kill_f2fs_super+0xe6/0x140
> > deactivate_locked_super+0x44/0xc0
> > deactivate_super+0x79/0x90
> > cleanup_mnt+0x114/0x1a0
> > __cleanup_mnt+0x16/0x20
> > task_work_run+0x98/0x100
> > exit_to_user_mode_prepare+0x3d0/0x3e0
> > syscall_exit_to_user_mode+0x12/0x30
> > do_syscall_64+0x42/0x80
> > entry_SYSCALL_64_after_hwframe+0x46/0xb0
> >
> > Function flow analysis when BUG occurs:
> > f2fs_fallocate mmap
> > do_page_fault
> > pte_spinlock // ---lock_pte
> > do_wp_page
> > wp_page_shared
> > pte_unmap_unlock // unlock_pte
> > do_page_mkwrite
> > f2fs_vm_page_mkwrite
> > down_read(i_mmap_sem)
> > lock_page
> > if (PageMappedToDisk(page))
> > goto out;
> > // set_page_dirty --NOT RUN
> > out: up_read(i_mmap_sem)
> > lock_page
> > finish_mkwrite_fault // unlock_pte
> > f2fs_collapse_range
> > down_write(i_mmap_sem)
> > truncate_pagecache
> > unmap_mapping_pages
> > i_mmap_lock_write // down_write(i_mmap_rwsem)
> > ......
> > zap_pte_range
> > pte_offset_map_lock // ---lock_pte
> > f2fs_set_data_page_dirty
>
> I didn't get it, why zap_pte_range() can set page dirty w/o lock_page?
>
> I found it's very easy to reproduce this bug, but previously I never saw this...
> is there any code udpate around truncate_pagecache()?
Found this.
2637 * The caller must ensure this doesn't race with truncation. Most will
2638 * simply hold the folio lock, but e.g. zap_pte_range() calls with the
2639 * folio mapped and the pte lock held, which also locks out truncation.
2640 */
2641 bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
2642 {
>
> Thanks,
>
> > if (!PageDirty(page)) {
> > fault_dirty_shared_page
> > f2fs_set_data_page_dirty
> > if (!PageDirty(page)) {
> > __set_page_dirty_nobuffer
> > f2fs_update_dirty_page // ++
> > }
> > unlock_page
> > __set_page_dirty_nobuffers
> > f2fs_update_dirty_page // page count++
> > }
> > pte_unmap_unlock // --unlock_pte
> > i_mmap_unlock_write // up_write(i_mmap_rwsem)
> > truncate_inode_pages
> > up_write(i_mmap_sem)
> >
> > When race happens between mmap-do_page_fault-wp_page_shared and
> > fallocate-truncate_pagecache-zap_pte_range, the zap_pte_range calls
> > function set_page_dirty without page lock. Besides, though
> > truncate_pagecache has immap and pte lock, wp_page_shared calls
> > fault_dirty_shared_page without any. In this case, two threads race
> > in f2fs_set_data_page_dirty function. Page is set to dirty only ONCE,
> > but the count is added TWICE by calling f2fs_update_dirty_page.
> > Thus the count of dirty page cannot accord with the real dirty pages.
> >
> > Following is the solution to in case of race happens without any lock.
> > If making sure f2fs_vm_page_mkwrite calls set_page_dirty within immap
> > lock area, page will already be dirtied when running into
> > fault_dirty_shared_page-f2fs_set_data_page_dirty.
> > The count of dirty page will not be increased wrong times.
> >
> > Signed-off-by: Shuqi Zhang <zhangshuqi3@...wei.com>
> > ---
> > fs/f2fs/file.c | 11 ++++++-----
> > 1 file changed, 6 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index ce4905a073b3..d837359a9c00 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -140,7 +140,7 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
> > * check to see if the page is mapped already (no holes)
> > */
> > if (PageMappedToDisk(page))
> > - goto out_sem;
> > + goto set_dirty;
> > /* page is wholly or partially inside EOF */
> > if (((loff_t)(page->index + 1) << PAGE_SHIFT) >
> > @@ -150,14 +150,15 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
> > offset = i_size_read(inode) & ~PAGE_MASK;
> > zero_user_segment(page, offset, PAGE_SIZE);
> > }
> > - set_page_dirty(page);
> > - if (!PageUptodate(page))
> > - SetPageUptodate(page);
> > f2fs_update_iostat(sbi, APP_MAPPED_IO, F2FS_BLKSIZE);
> > - f2fs_update_time(sbi, REQ_TIME);
> > +set_dirty:
> > trace_f2fs_vm_page_mkwrite(page, DATA);
> > + set_page_dirty(page);
> > + if (!PageUptodate(page))
> > + SetPageUptodate(page);
> > + f2fs_update_time(sbi, REQ_TIME);
> > out_sem:
> > filemap_invalidate_unlock_shared(inode->i_mapping);
Powered by blists - more mailing lists