[PATCH AUTOSEL 5.4 1/2] ext4: don't BUG if someone dirty pages without asking ext4 first

[PATCH AUTOSEL 5.4 1/2] ext4: don't BUG if someone dirty pages without asking ext4 first

[Sasha Levin]

From: Theodore Ts'o <tytso@mit.edu>

[ 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>
---
 fs/ext4/inode.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index dcbd8ac8d471..0d62f05f8925 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2161,6 +2161,15 @@ 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
@@ -2710,6 +2719,22 @@ 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;
-- 
2.34.1

[PATCH AUTOSEL 5.4 2/2] ntfs: add sanity check on allocation size

[Sasha Levin]

From: Dongliang Mu <mudongliangabcd@gmail.com>

[ Upstream commit 714fbf2647b1a33d914edd695d4da92029c7e7c0 ]

ntfs_read_inode_mount invokes ntfs_malloc_nofs with zero allocation
size.  It triggers one BUG in the __ntfs_malloc function.

Fix this by adding sanity check on ni->attr_list_size.

Link: https://lkml.kernel.org/r/20220120094914.47736-1-dzm91@hust.edu.cn
Reported-by: syzbot+3c765c5248797356edaa@syzkaller.appspotmail.com
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Acked-by: Anton Altaparmakov <anton@tuxera.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ntfs/inode.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
index ea18e4a2a691..cf222c9225d6 100644
--- a/fs/ntfs/inode.c
+++ b/fs/ntfs/inode.c
@@ -1881,6 +1881,10 @@ int ntfs_read_inode_mount(struct inode *vi)
 		}
 		/* Now allocate memory for the attribute list. */
 		ni->attr_list_size = (u32)ntfs_attr_size(a);
+		if (!ni->attr_list_size) {
+			ntfs_error(sb, "Attr_list_size is zero");
+			goto put_err_out;
+		}
 		ni->attr_list = ntfs_malloc_nofs(ni->attr_list_size);
 		if (!ni->attr_list) {
 			ntfs_error(sb, "Not enough memory to allocate buffer "
-- 
2.34.1

Re: [PATCH AUTOSEL 5.4 1/2] ext4: don't BUG if someone dirty pages without asking ext4 first

[syzbot]

> From: Theodore Ts'o <tytso@mit.edu>
>
> [ 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>
> ---
>  fs/ext4/inode.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index dcbd8ac8d471..0d62f05f8925 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2161,6 +2161,15 @@ 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
> @@ -2710,6 +2719,22 @@ 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;
> -- 
> 2.34.1
>

I see the command but can't find the corresponding bug.
The email is sent to  syzbot+HASH@syzkaller.appspotmail.com address
but the HASH does not correspond to any known bug.
Please double check the address.