On 2024/2/20 13:39, Ojaswin Mujoo wrote:
On Fri, Jan 26, 2024 at 04:57:14PM +0800, Baokun Li wrote:
Hey Baokun,
Good catch! I've added some minor comments below. Other than that feel free to add
Reviewed-by: Ojaswin Mujoo ojaswin@linux.ibm.com
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@vger.kernel.org Signed-off-by: Baokun Li libaokun1@huawei.com
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; }
So along with this change, I think it'll also be good to add an extra check in ext4_mb_choose_next_group_best_avail() as:
if (1 << min_order < ac->ac_o_ex.fe_len) min_order = fls(ac->ac_o_ex.fe_len);
- if (order >= MB_NUM_ORDERS(ac->ac_sb))
- order = MB_NUM_ORDERS(ac->ac_sb) - 1;
- for (i = order; i >= min_order; i--) { int frag_order; /*
The reason for this is that otherwise when order is large eg 29, we would unnecessarily loop from i=29 to i=13 while always looking at the same avg_fragment_list[13].
Regards, ojaswin
Yeah, good point! This will cut down on some unnecessary loops.
I'll add this extra check in the next version.
Thanks for having a look!