linux-kernel - Re: [PATCH] ext4: fix potential null deref in ext4_mb

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Message-ID: <175892300640.128029.5686356472247725279.b4-ty@mit.edu>
Date: Fri, 26 Sep 2025 17:47:42 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: linux-ext4@...r.kernel.org, libaokun@...weicloud.com
Cc: "Theodore Ts'o" <tytso@....edu>, adilger.kernel@...ger.ca, jack@...e.cz,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        yangerkun@...wei.com, libaokun1@...wei.com,
        syzbot+1713b1aa266195b916c2@...kaller.appspotmail.com
Subject: Re: [PATCH] ext4: fix potential null deref in ext4_mb_init()


On Mon, 25 Aug 2025 11:38:30 +0800, libaokun@...weicloud.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@....edu>