On 8/25/2025 11:38 AM, libaokun@xxxxxxxxxxxxxxx wrote: > From: Baokun Li <libaokun1@xxxxxxxxxx> > > In ext4_mb_init(), ext4_mb_avg_fragment_size_destroy() may be called > when sbi->s_mb_avg_fragment_size remains uninitialized (e.g., if groupinfo > slab cache allocation fails). Since ext4_mb_avg_fragment_size_destroy() > lacks null pointer checking, this leads to a null pointer dereference. > > ================================================================== > EXT4-fs: no memory for groupinfo slab cache > BUG: kernel NULL pointer dereference, address: 0000000000000000 > PGD 0 P4D 0 > Oops: Oops: 0002 [#1] SMP PTI > CPU:2 UID: 0 PID: 87 Comm:mount Not tainted 6.17.0-rc2 #1134 PREEMPT(none) > RIP: 0010:_raw_spin_lock_irqsave+0x1b/0x40 > Call Trace: > <TASK> > xa_destroy+0x61/0x130 > ext4_mb_init+0x483/0x540 > __ext4_fill_super+0x116d/0x17b0 > ext4_fill_super+0xd3/0x280 > get_tree_bdev_flags+0x132/0x1d0 > vfs_get_tree+0x29/0xd0 > do_new_mount+0x197/0x300 > __x64_sys_mount+0x116/0x150 > do_syscall_64+0x50/0x1c0 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > ================================================================== > > Therefore, add necessary null check to ext4_mb_avg_fragment_size_destroy() > to prevent this issue. The same fix is also applied to > ext4_mb_largest_free_orders_destroy(). > > Reported-by: syzbot+1713b1aa266195b916c2@xxxxxxxxxxxxxxxxxxxxxxxxx > Closes: https://syzkaller.appspot.com/bug?extid=1713b1aa266195b916c2 > Fixes: f7eaacbb4e54 ("ext4: convert free groups order lists to xarrays") > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx> Looks good to me. Reviewed-by: Zhang Yi <yi.zhang@xxxxxxxxxx> > --- > fs/ext4/mballoc.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index 5898d92ba19f..6070d3c86678 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -3655,16 +3655,26 @@ static void ext4_discard_work(struct work_struct *work) > > static inline void ext4_mb_avg_fragment_size_destroy(struct ext4_sb_info *sbi) > { > + if (!sbi->s_mb_avg_fragment_size) > + return; > + > for (int i = 0; i < MB_NUM_ORDERS(sbi->s_sb); i++) > xa_destroy(&sbi->s_mb_avg_fragment_size[i]); > + > kfree(sbi->s_mb_avg_fragment_size); > + sbi->s_mb_avg_fragment_size = NULL; > } > > static inline void ext4_mb_largest_free_orders_destroy(struct ext4_sb_info *sbi) > { > + if (!sbi->s_mb_largest_free_orders) > + return; > + > for (int i = 0; i < MB_NUM_ORDERS(sbi->s_sb); i++) > xa_destroy(&sbi->s_mb_largest_free_orders[i]); > + > kfree(sbi->s_mb_largest_free_orders); > + sbi->s_mb_largest_free_orders = NULL; > } > > int ext4_mb_init(struct super_block *sb)
