Re: Patch "ext4: fix slab-out-of-bounds in ext4_mb_find_good_group_avg_frag_lists()" has been added to the 6.9-stable tree

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jun 17, 2024 at 09:37:01AM +0800, Baokun Li wrote:
> Hi Sasha,
> 
> Thanks for adapting this patch to the stable branch. Just one nit.
> 
> On 2024/6/16 10:05, Sasha Levin wrote:
> > This is a note to let you know that I've just added the patch titled
> > 
> >      ext4: fix slab-out-of-bounds in ext4_mb_find_good_group_avg_frag_lists()
> > 
> > to the 6.9-stable tree which can be found at:
> >      http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> > 
> > The filename of the patch is:
> >       ext4-fix-slab-out-of-bounds-in-ext4_mb_find_good_gro.patch
> > and it can be found in the queue-6.9 subdirectory.
> > 
> > If you, or anyone else, feels it should not be added to the stable tree,
> > please let <stable@vger.kernel.org> know about it.
> > 
> > 
> > 
> > commit 84cee2d2394a43766dd2990edac8a4a05817ef7b
> > Author: Baokun Li <libaokun1@huawei.com>
> > Date:   Tue Mar 19 19:33:20 2024 +0800
> > 
> >      ext4: fix slab-out-of-bounds in ext4_mb_find_good_group_avg_frag_lists()
> >      [ Upstream commit 13df4d44a3aaabe61cd01d277b6ee23ead2a5206 ]
> >      We can trigger a slab-out-of-bounds with the following commands:
> >          mkfs.ext4 -F /dev/$disk 10G
> >          mount /dev/$disk /tmp/test
> >          echo 2147483647 > /sys/fs/ext4/$disk/mb_group_prealloc
> >          echo test > /tmp/test/file && sync
> >      ==================================================================
> >      BUG: KASAN: slab-out-of-bounds in ext4_mb_find_good_group_avg_frag_lists+0x8a/0x200 [ext4]
> >      Read of size 8 at addr ffff888121b9d0f0 by task kworker/u2:0/11
> >      CPU: 0 PID: 11 Comm: kworker/u2:0 Tainted: GL 6.7.0-next-20240118 #521
> >      Call Trace:
> >       dump_stack_lvl+0x2c/0x50
> >       kasan_report+0xb6/0xf0
> >       ext4_mb_find_good_group_avg_frag_lists+0x8a/0x200 [ext4]
> >       ext4_mb_regular_allocator+0x19e9/0x2370 [ext4]
> >       ext4_mb_new_blocks+0x88a/0x1370 [ext4]
> >       ext4_ext_map_blocks+0x14f7/0x2390 [ext4]
> >       ext4_map_blocks+0x569/0xea0 [ext4]
> >       ext4_do_writepages+0x10f6/0x1bc0 [ext4]
> >      [...]
> >      ==================================================================
> >      The flow of issue triggering is as follows:
> >      // Set s_mb_group_prealloc to 2147483647 via sysfs
> >      ext4_mb_new_blocks
> >        ext4_mb_normalize_request
> >          ext4_mb_normalize_group_request
> >            ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc
> >        ext4_mb_regular_allocator
> >          ext4_mb_choose_next_group
> >            ext4_mb_choose_next_group_best_avail
> >              mb_avg_fragment_size_order
> >                order = fls(len) - 2 = 29
> >              ext4_mb_find_good_group_avg_frag_lists
> >                frag_list = &sbi->s_mb_avg_fragment_size[order]
> >                if (list_empty(frag_list)) // Trigger SOOB!
> >      At 4k block size, the length of the s_mb_avg_fragment_size list is 14,
> >      but an oversized s_mb_group_prealloc is set, causing slab-out-of-bounds
> >      to be triggered by an attempt to access an element at index 29.
> >      Add a new attr_id attr_clusters_in_group with values in the range
> >      [0, sbi->s_clusters_per_group] and declare mb_group_prealloc as
> >      that type to fix the issue. In addition avoid returning an order
> >      from mb_avg_fragment_size_order() greater than MB_NUM_ORDERS(sb)
> >      and reduce some useless loops.
> >      Fixes: 7e170922f06b ("ext4: Add allocation criteria 1.5 (CR1_5)")
> >      CC: stable@vger.kernel.org
> >      Signed-off-by: Baokun Li <libaokun1@huawei.com>
> >      Reviewed-by: Jan Kara <jack@suse.cz>
> >      Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
> >      Link: https://lore.kernel.org/r/20240319113325.3110393-5-libaokun1@huawei.com
> >      Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> >      Signed-off-by: Sasha Levin <sashal@kernel.org>
> > 
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index 714f83632e3f9..66b5a68b0254e 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -831,6 +831,8 @@ static int mb_avg_fragment_size_order(struct super_block *sb, ext4_grpblk_t len)
> >   		return 0;
> >   	if (order == MB_NUM_ORDERS(sb))
> >   		order--;
> > +	if (WARN_ON_ONCE(order > MB_NUM_ORDERS(sb)))
> > +		order = MB_NUM_ORDERS(sb) - 1;
> >   	return order;
> >   }
> > @@ -1008,6 +1010,8 @@ static void ext4_mb_choose_next_group_best_avail(struct ext4_allocation_context
> >   	 * goal length.
> >   	 */
> >   	order = fls(ac->ac_g_ex.fe_len) - 1;
> > +	if (WARN_ON_ONCE(order - 1 > MB_NUM_ORDERS(ac->ac_sb)))
> > +		order = MB_NUM_ORDERS(ac->ac_sb);
> >   	min_order = order - sbi->s_mb_best_avail_max_trim_order;
> >   	if (min_order < 0)
> >   		min_order = 0;
> > diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> > index 295ea9a32de91..ca66e33f61815 100644
> > --- a/fs/ext4/sysfs.c
> > +++ b/fs/ext4/sysfs.c
> > @@ -29,6 +29,7 @@ typedef enum {
> >   	attr_trigger_test_error,
> >   	attr_first_error_time,
> >   	attr_last_error_time,
> > +	attr_clusters_in_group,
> >   	attr_feature,
> >   	attr_pointer_ui,
> >   	attr_pointer_ul,
> > @@ -207,13 +208,14 @@ EXT4_ATTR_FUNC(sra_exceeded_retry_limit, 0444);
> >   EXT4_ATTR_OFFSET(inode_readahead_blks, 0644, inode_readahead,
> >   		 ext4_sb_info, s_inode_readahead_blks);
> > +EXT4_ATTR_OFFSET(mb_group_prealloc, 0644, clusters_in_group,
> > +		 ext4_sb_info, s_mb_group_prealloc);
> >   EXT4_RW_ATTR_SBI_UI(inode_goal, s_inode_goal);
> >   EXT4_RW_ATTR_SBI_UI(mb_stats, s_mb_stats);
> >   EXT4_RW_ATTR_SBI_UI(mb_max_to_scan, s_mb_max_to_scan);
> >   EXT4_RW_ATTR_SBI_UI(mb_min_to_scan, s_mb_min_to_scan);
> >   EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
> >   EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
> > -EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
> >   EXT4_RW_ATTR_SBI_UI(mb_max_linear_groups, s_mb_max_linear_groups);
> >   EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
> >   EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error);
> > @@ -376,6 +378,7 @@ static ssize_t ext4_generic_attr_show(struct ext4_attr *a,
> >   	switch (a->attr_id) {
> >   	case attr_inode_readahead:
> > +	case attr_clusters_in_group:
> >   	case attr_pointer_ui:
> >   		if (a->attr_ptr == ptr_ext4_super_block_offset)
> >   			return sysfs_emit(buf, "%u\n", le32_to_cpup(ptr));
> > @@ -459,6 +462,14 @@ static ssize_t ext4_attr_store(struct kobject *kobj,
> >   		else
> >   			*((unsigned int *) ptr) = t;
> >   		return len;
> > +	case attr_clusters_in_group:
> Since commit f536808adcc3 "ext4: refactor out ext4_generic_attr_store()"
> is not backported to stable, the following judgement needs to be added
> here:
> 
>  		if (!ptr)
>  			return 0;
> 
> The patch for the 6.6-stable tree has the same problem.

Thanks, I've dropped this from both queues now, can you resend it with a
fixed up version?

thanks,

greg k-h