Re: [PATCH 2/2] ext4: add inode table check in __ext4_get_inode_loc to aovid possible infinite loop

[Ritesh Harjani (IBM)]

On 22/08/17 04:31PM, Jan Kara wrote:
> On Wed 17-08-22 21:27:01, Baokun Li wrote:
> > In do_writepages, if the value returned by ext4_writepages is "-ENOMEM"
> > and "wbc->sync_mode == WB_SYNC_ALL", retry until the condition is not met.
> >
> > In __ext4_get_inode_loc, if the bh returned by sb_getblk is NULL,
> > the function returns -ENOMEM.
> >
> > In __getblk_slow, if the return value of grow_buffers is less than 0,
> > the function returns NULL.
> >
> > When the three processes are connected in series like the following stack,
> > an infinite loop may occur:
> >
> > do_writepages					<--- keep retrying
> >  ext4_writepages
> >   mpage_map_and_submit_extent
> >    mpage_map_one_extent
> >     ext4_map_blocks
> >      ext4_ext_map_blocks
> >       ext4_ext_handle_unwritten_extents
> >        ext4_ext_convert_to_initialized
> >         ext4_split_extent
> >          ext4_split_extent_at
> >           __ext4_ext_dirty
> >            __ext4_mark_inode_dirty
> >             ext4_reserve_inode_write
> >              ext4_get_inode_loc
> >               __ext4_get_inode_loc		<--- return -ENOMEM
> >                sb_getblk
> >                 __getblk_gfp
> >                  __getblk_slow			<--- return NULL
> >                   grow_buffers
> >                    grow_dev_page		<--- return -ENXIO
> >                     ret = (block < end_block) ? 1 : -ENXIO;
> >
> > In this issue, bg_inode_table_hi is overwritten as an incorrect value.
> > As a result, `block < end_block` cannot be met in grow_dev_page.
> > Therefore, __ext4_get_inode_loc always returns '-ENOMEM' and do_writepages
> > keeps retrying. As a result, the writeback process is in the D state due
> > to an infinite loop.
> >
> > Add a check on inode table block in the __ext4_get_inode_loc function by
> > referring to ext4_read_inode_bitmap to avoid this infinite loop.
> >
> > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
>
> Thanks for the fixes. Normally, we check that inode table is fine in
> ext4_check_descriptors() (and those checks are much stricter) so it seems
> unnecessary to check it again here. I understand that in your case it was
> resize that corrupted the group descriptor after the filesystem was mounted
> which is nasty but there's much more metadata that can be corrupted like
> this and it's infeasible to check each metadata block before we use it.
>
> IMHO a proper fix to this class of issues would be for sb_getblk() to
> return proper error so that we can distinguish ENOMEM from other errors.
> But that will be a larger undertaking...
>

Hi Jan,

How about adding a wrapper around sb_getblk() which will do the basic block
bound checks for ext4. Then we can carefully convert all the callers of
sb_getblk() in ext4 to call ext4_sb_getblk().

ext4_sb_getblk() will then return either of below -
1. ERR_PTR(-EFSCORRUPTED)
2. NULL
3. struct buffer_head*

It's caller can then implement the proper error handling.

Folding a small patch to implement the simple bound check. Is this the right
approach?

From: "Ritesh Harjani (IBM)" <ritesh.list@xxxxxxxxx>
Date: Thu, 18 Aug 2022 07:53:58 -0500
Subject: [RFC] ext4: Add ext4_sb_getblk() wrapper for block bounds checking

We might need more bounds checking on the block before calling sb_getblk().
This helper does that and if it is not valid then returns ERR_PTR(-EFSCORRUPTED)
Later we will need to carefully convert the callers to use ext4_sb_getblk()
instead of sb_getblk().
For e.g. __ext4_get_inode_loc()

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
---
 fs/ext4/block_validity.c |  4 +---
 fs/ext4/ext4.h           | 12 ++++++++++++
 fs/ext4/super.c          |  9 +++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
index 5504f72bbbbe..69347fab7c38 100644
--- a/fs/ext4/block_validity.c
+++ b/fs/ext4/block_validity.c
@@ -301,9 +301,7 @@ int ext4_sb_block_valid(struct super_block *sb, struct inode *inode,
 	struct rb_node *n;
 	int ret = 1;

-	if ((start_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
-	    (start_blk + count < start_blk) ||
-	    (start_blk + count > ext4_blocks_count(sbi->s_es)))
+	if (!ext4_sb_block_valid_fastcheck(sbi->s_es, start_blk, count))
 		return 0;

 	/*
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 9bca5565547b..79d0e45185d3 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3072,6 +3072,8 @@ extern struct buffer_head *ext4_sb_bread(struct super_block *sb,
 					 sector_t block, blk_opf_t op_flags);
 extern struct buffer_head *ext4_sb_bread_unmovable(struct super_block *sb,
 						   sector_t block);
+extern struct buffer_head *ext4_sb_getblk(struct super_block *sb,
+					  sector_t block);
 extern void ext4_read_bh_nowait(struct buffer_head *bh, blk_opf_t op_flags,
 				bh_end_io_t *end_io);
 extern int ext4_read_bh(struct buffer_head *bh, blk_opf_t op_flags,
@@ -3358,6 +3360,16 @@ static inline unsigned int ext4_flex_bg_size(struct ext4_sb_info *sbi)
 	return 1 << sbi->s_log_groups_per_flex;
 }

+static inline bool ext4_sb_block_valid_fastcheck(struct ext4_super_block *es,
+					sector_t start_blk, unsigned int count)
+{
+	if ((start_blk <= le32_to_cpu(es->s_first_data_block)) ||
+	    (start_blk + count < start_blk) ||
+	    (start_blk + count > ext4_blocks_count(es)))
+		return false;
+	return true;
+}
+
 #define ext4_std_error(sb, errno)				\
 do {								\
 	if ((errno))						\
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 9a66abcca1a8..5b29272ad9a9 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -269,6 +269,15 @@ void ext4_sb_breadahead_unmovable(struct super_block *sb, sector_t block)
 	}
 }

+struct buffer_head *ext4_sb_getblk(struct super_block *sb, sector_t block)
+{
+	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
+
+	if (!ext4_sb_block_valid_fastcheck(es, block, 1))
+		return ERR_PTR(-EFSCORRUPTED);
+	return sb_getblk(sb, block);
+}
+
 static int ext4_verify_csum_type(struct super_block *sb,
 				 struct ext4_super_block *es)
 {
--
2.25.1

-ritesh



> 								Honza
>
> > ---
> >  fs/ext4/inode.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 601214453c3a..5e171879fa23 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -4466,9 +4466,17 @@ static int __ext4_get_inode_loc(struct super_block *sb, unsigned long ino,
> >  	inodes_per_block = EXT4_SB(sb)->s_inodes_per_block;
> >  	inode_offset = ((ino - 1) %
> >  			EXT4_INODES_PER_GROUP(sb));
> > -	block = ext4_inode_table(sb, gdp) + (inode_offset / inodes_per_block);
> >  	iloc->offset = (inode_offset % inodes_per_block) * EXT4_INODE_SIZE(sb);
> >
> > +	block = ext4_inode_table(sb, gdp);
> > +	if ((block <= le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block)) ||
> > +	    (block >= ext4_blocks_count(EXT4_SB(sb)->s_es))) {
> > +		ext4_error(sb, "Invalid inode table block %llu in "
> > +			   "block_group %u", block, iloc->block_group);
> > +		return -EFSCORRUPTED;
> > +	}
> > +	block += (inode_offset / inodes_per_block);
> > +
> >  	bh = sb_getblk(sb, block);
> >  	if (unlikely(!bh))
> >  		return -ENOMEM;
> > --
> > 2.31.1
> >
> --
> Jan Kara <jack@xxxxxxxx>
> SUSE Labs, CR