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/
Regards,
Baokun
+ ret = kstrtouint(skip_spaces(buf), 0, &t);
+ if (ret)
+ return ret;
+ if (t > sbi->s_clusters_per_group)
+ return -EINVAL;
+ *((unsigned int *) ptr) = t;
+ return len;
case attr_pointer_ul:
if (!ptr)
return 0;
