Re: [PATCH] ext4: fix potential null deref in ext4_mb_init()

Theodore Ts'o
2025-09-26T21:48:27Z

On Mon, 25 Aug 2025 11:38:30 +0800, libaokun@huaweicloud.com wrote:
> 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
> ==================================================================
>
> [...]

Applied, thanks!

[1/1] ext4: fix potential null deref in ext4_mb_init()
commit: 3c3fac6bc0a9c00dbe65d8dc0d3a282afe4d3188

Best regards,
--
Theodore Ts'o <tytso@mit.edu>