On Tue, Jul 16, 2024 at 10:11:55AM +0800, Baokun Li wrote:
> On 2024/6/19 20:19, libaokun@xxxxxxxxxxxxxxx wrote:
> > From: Baokun Li <libaokun1@xxxxxxxxxx>
> >
> > [ 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@xxxxxxxxxxxxxxx
> > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
> > Reviewed-by: Jan Kara <jack@xxxxxxx>
> > Reviewed-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
> > Link: https://lore.kernel.org/r/20240319113325.3110393-5-libaokun1@xxxxxxxxxx
> > Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
> > ---
> > fs/ext4/mballoc.c | 4 ++++
> > fs/ext4/sysfs.c | 15 ++++++++++++++-
> > 2 files changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index 714f83632e3f..66b5a68b0254 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 ca820620b974..d65dccb44ed5 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);
> > @@ -392,6 +394,7 @@ static ssize_t ext4_attr_show(struct kobject *kobj,
> > (unsigned long long)
> > percpu_counter_sum(&sbi->s_sra_exceeded_retry_limit));
> > case attr_inode_readahead:
> > + case attr_clusters_in_group:
> > case attr_pointer_ui:
> > if (!ptr)
> > return 0;
> > @@ -469,6 +472,16 @@ static ssize_t ext4_attr_store(struct kobject *kobj,
> > else
> > *((unsigned int *) ptr) = t;
> > return len;
> > + case attr_clusters_in_group:
>
> Hi Greg,
>
> > + if (!ptr)
> > + return 0;
>
> I've found that the commit that eventually gets merged in doesn't have this
> judgment.
>
> 6.6: 677ff4589f15 ("ext4: fix slab-out-of-bounds in
> ext4_mb_find_good_group_avg_frag_lists()")
> 6.9: b829687ae122 ("ext4: fix slab-out-of-bounds in
> ext4_mb_find_good_group_avg_frag_lists()")
>
> This may result in a null pointer dereference.
>
>
> History:
> https://lore.kernel.org/all/0d620010-c6b4-4f80-a835-451813f957e3@xxxxxxxxxx/
> https://lore.kernel.org/all/20240619121952.3508695-2-libaokun@xxxxxxxxxxxxxxx/
> https://lore.kernel.org/all/20240625085542.189183696@xxxxxxxxxxxxxxxxxxx/
I don't understand, can you send a patch that fixes this?
Or should we just revert the original commits? If so, what commit ids
need to be reverted?
thanks,
greg k-h
