[PATCH] lib/ext2fs: Validity checks for ext2fs_inode_scan_goto_blockgroup()

[PATCH] lib/ext2fs: Validity checks for ext2fs_inode_scan_goto_blockgroup()

[Brian Norris]

We don't validate the 'group' argument, so it's easy to get underflows
or crashes here.

This resolves issues seen in ureadahead, when it uses an old packfile
(with mismatching group indices) with a new filesystem.

Signed-off-by: Brian Norris <briannorris@chromium.org>
---

 lib/ext2fs/inode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/ext2fs/inode.c b/lib/ext2fs/inode.c
index 957d5aa9f9d6..96d854b5fb69 100644
--- a/lib/ext2fs/inode.c
+++ b/lib/ext2fs/inode.c
@@ -313,6 +313,9 @@ static errcode_t get_next_blockgroup(ext2_inode_scan scan)
 errcode_t ext2fs_inode_scan_goto_blockgroup(ext2_inode_scan scan,
 					    int	group)
 {
+	if (group <= 0 || group >= scan->fs->group_desc_count)
+		return EXT2_ET_INVALID_ARGUMENT;
+
 	scan->current_group = group - 1;
 	scan->groups_left = scan->fs->group_desc_count - group;
 	scan->bad_block_ptr = 0;
-- 
2.43.0.rc2.451.g8631bc7472-goog

Re: [PATCH] lib/ext2fs: Validity checks for ext2fs_inode_scan_goto_blockgroup()

[Darrick J. Wong]

On Thu, Nov 30, 2023 at 04:01:18PM -0800, Brian Norris wrote:
> We don't validate the 'group' argument, so it's easy to get underflows
> or crashes here.
> 
> This resolves issues seen in ureadahead, when it uses an old packfile
> (with mismatching group indices) with a new filesystem.

Say what now?  The boot time pre-caching thing Ubuntu used to have?
https://manpages.ubuntu.com/manpages/trusty/man8/ureadahead.8.html

--D

> Signed-off-by: Brian Norris <briannorris@chromium.org>
> ---
> 
>  lib/ext2fs/inode.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/lib/ext2fs/inode.c b/lib/ext2fs/inode.c
> index 957d5aa9f9d6..96d854b5fb69 100644
> --- a/lib/ext2fs/inode.c
> +++ b/lib/ext2fs/inode.c
> @@ -313,6 +313,9 @@ static errcode_t get_next_blockgroup(ext2_inode_scan scan)
>  errcode_t ext2fs_inode_scan_goto_blockgroup(ext2_inode_scan scan,
>  					    int	group)
>  {
> +	if (group <= 0 || group >= scan->fs->group_desc_count)
> +		return EXT2_ET_INVALID_ARGUMENT;
> +
>  	scan->current_group = group - 1;
>  	scan->groups_left = scan->fs->group_desc_count - group;
>  	scan->bad_block_ptr = 0;
> -- 
> 2.43.0.rc2.451.g8631bc7472-goog
> 
> 

Re: [PATCH] lib/ext2fs: Validity checks for ext2fs_inode_scan_goto_blockgroup()

[Brian Norris]

On Fri, Dec 1, 2023 at 8:24 AM Darrick J. Wong <djwong@kernel.org> wrote:
> On Thu, Nov 30, 2023 at 04:01:18PM -0800, Brian Norris wrote:
> > This resolves issues seen in ureadahead, when it uses an old packfile
> > (with mismatching group indices) with a new filesystem.
>
> Say what now?  The boot time pre-caching thing Ubuntu used to have?
> https://manpages.ubuntu.com/manpages/trusty/man8/ureadahead.8.html

Sure. ChromeOS still uses it. Steven Rostedt even bothered to do a
talk about it recently:
https://eoss2023.sched.com/event/1LcMw/the-resurrection-of-ureadahead-and-speeding-up-the-boot-process-and-preloading-applications-steven-rostedt-google

Brian

Re: [PATCH] lib/ext2fs: Validity checks for ext2fs_inode_scan_goto_blockgroup()

[Darrick J. Wong]

On Fri, Dec 01, 2023 at 09:30:38AM -0800, Brian Norris wrote:
> On Fri, Dec 1, 2023 at 8:24 AM Darrick J. Wong <djwong@kernel.org> wrote:
> > On Thu, Nov 30, 2023 at 04:01:18PM -0800, Brian Norris wrote:
> > > This resolves issues seen in ureadahead, when it uses an old packfile
> > > (with mismatching group indices) with a new filesystem.
> >
> > Say what now?  The boot time pre-caching thing Ubuntu used to have?
> > https://manpages.ubuntu.com/manpages/trusty/man8/ureadahead.8.html
> 
> Sure. ChromeOS still uses it. Steven Rostedt even bothered to do a
> talk about it recently:
> https://eoss2023.sched.com/event/1LcMw/the-resurrection-of-ureadahead-and-speeding-up-the-boot-process-and-preloading-applications-steven-rostedt-google

Wow.  I had no idea that ureadahead reads the inode blocks of a mounted
ext* filesystem into the page cache.  Welp, it's a good thing those are
part of the static layout.

Anyway, this fix looks correct to me, so I don't see any reason to hold
this up...
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> 
> Brian
>