From: Theodore Ts'o tytso@mit.edu
stable inclusion from stable-v5.10.110 commit 330d0e44fc5a47c27df958ecdd4693a3cb1d8b81 bugzilla: https://gitee.com/openeuler/kernel/issues/I574AL
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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[ Upstream commit cc5095747edfb054ca2068d01af20be3fcc3634f ]
[un]pin_user_pages_remote is dirtying pages without properly warning the file system in advance. A related race was noted by Jan Kara in 2018[1]; however, more recently instead of it being a very hard-to-hit race, it could be reliably triggered by process_vm_writev(2) which was discovered by Syzbot[2].
This is technically a bug in mm/gup.c, but arguably ext4 is fragile in that if some other kernel subsystem dirty pages without properly notifying the file system using page_mkwrite(), ext4 will BUG, while other file systems will not BUG (although data will still be lost).
So instead of crashing with a BUG, issue a warning (since there may be potential data loss) and just mark the page as clean to avoid unprivileged denial of service attacks until the problem can be properly fixed. More discussion and background can be found in the thread starting at [2].
[1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz [2] https://lore.kernel.org/r/Yg0m6IjcNmfaSokM@google.com
Reported-by: syzbot+d59332e2db681cf18f0318a06e994ebbb529a8db@syzkaller.appspotmail.com Reported-by: Lee Jones lee.jones@linaro.org Signed-off-by: Theodore Ts'o tytso@mit.edu Link: https://lore.kernel.org/r/YiDS9wVfq4mM2jGK@mit.edu Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Yu Liao liaoyu15@huawei.com Reviewed-by: Wei Li liwei391@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- fs/ext4/inode.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index a057b9f54bda..a46b0074ebcc 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2019,6 +2019,15 @@ static int ext4_writepage(struct page *page, else len = PAGE_SIZE;
+ /* Should never happen but for bugs in other kernel subsystems */ + if (!page_has_buffers(page)) { + ext4_warning_inode(inode, + "page %lu does not have buffers attached", page->index); + ClearPageDirty(page); + unlock_page(page); + return 0; + } + page_bufs = page_buffers(page); /* * We cannot do block allocation or other extent handling in this @@ -2628,6 +2637,22 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd) wait_on_page_writeback(page); BUG_ON(PageWriteback(page));
+ /* + * Should never happen but for buggy code in + * other subsystems that call + * set_page_dirty() without properly warning + * the file system first. See [1] for more + * information. + * + * [1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz + */ + if (!page_has_buffers(page)) { + ext4_warning_inode(mpd->inode, "page %lu does not have buffers attached", page->index); + ClearPageDirty(page); + unlock_page(page); + continue; + } + if (mpd->map.m_len == 0) mpd->first_page = page->index; mpd->next_page = page->index + 1;