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.
Therefore it is not allowed to set s_mb_group_prealloc to a value greater
than s_clusters_per_group via sysfs, and to avoid returning an order from
mb_avg_fragment_size_order() that is greater than MB_NUM_ORDERS(sb).
Fixes: 7e170922f06b ("ext4: Add allocation criteria 1.5 (CR1_5)")
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
fs/ext4/mballoc.c | 2 ++
fs/ext4/sysfs.c | 9 ++++++++-
2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index f44f668e407f..1ea6491b6b00 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -832,6 +832,8 @@ 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;
}
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index 6f9f96e00f2f..60ca7b2797b2 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_group_prealloc,
attr_feature,
attr_pointer_pi,
attr_pointer_ui,
@@ -211,13 +212,14 @@ 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, group_prealloc,
+ 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_PI(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);
@@ -380,6 +382,7 @@ static ssize_t ext4_generic_attr_show(struct ext4_attr *a,
switch (a->attr_id) {
case attr_inode_readahead:
+ case attr_group_prealloc:
case attr_pointer_pi:
case attr_pointer_ui:
if (a->attr_ptr == ptr_ext4_super_block_offset)
@@ -453,6 +456,10 @@ static ssize_t ext4_generic_attr_store(struct ext4_attr *a,
return ret;
switch (a->attr_id) {
+ case attr_group_prealloc:
+ if (t > sbi->s_clusters_per_group)
+ return -EINVAL;
+ fallthrough;
case attr_pointer_pi:
if ((int)t < 0)
return -EINVAL;
--
2.31.1
