Hi Jan,
On 2024/3/14 18:30, Jan Kara wrote:
On Tue 27-02-24 17:11:43, Baokun Li wrote:
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 Looks good. Just one nit below. Otherwise feel free to add:
Reviewed-by: Jan Kara jack@suse.cz
fs/ext4/mballoc.c | 6 ++++++ fs/ext4/sysfs.c | 13 ++++++++++++- 2 files changed, 18 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 85a91a61b761..7ad089df2408 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;@@ -1057,6 +1059,10 @@ static void ext4_mb_choose_next_group_best_avail(struct ext4_allocation_context ac->ac_flags |= EXT4_MB_CR_BEST_AVAIL_LEN_OPTIMIZED; return; }
/* Skip some unnecessary loops. */if (unlikely(i > MB_NUM_ORDERS(ac->ac_sb)))i = MB_NUM_ORDERS(ac->ac_sb);How can this possibly trigger now? MB_NUM_ORDERS is sb->s_blocksize_bits + 2. 'i' is starting at fls(ac->ac_g_ex.fe_len) and ac_g_ex.fe_len shouldn't be larger than clusters per group, hence fls() should be less than sb->s_blocksize_bits? Am I missing something? And if yes, we should rather make sure 'order' is never absurdly big?
I suspect this code is defensive upto a point of being confusing :)
Honza
Yes, this is indeed defensive code! Only walk into this branch when WARN_ON_ONCE(order > MB_NUM_ORDERS(sb)) is triggered. As previously mentioned by ojaswin in the following link:
"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]."
Link：https://lore.kernel.org/lkml/ZdQ7FEA7KC4eAMpg@li-bb2b2a4c-3307-11b2-a85c-8fa...
Thank you so much for the review! ღ( ´･ᴗ･` )