linux-kernel - Re: [PATCH] jfs: set diskblock and maxag to zero when creating imap

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Message-ID: <046f91fc-dc84-48de-b2e0-9f072283facd@oracle.com>
Date: Wed, 19 Feb 2025 16:54:05 -0600
From: Dave Kleikamp <dave.kleikamp@...cle.com>
To: Edward Adam Davis <eadavis@...com>,
        syzbot+df6cdcb35904203d2b6d@...kaller.appspotmail.com
Cc: jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] jfs: set diskblock and maxag to zero when creating imap

On 2/19/25 8:08AM, Edward Adam Davis wrote:
> syzbot reported a uninit-value in diFree. [1]
> 
> When print_hex_dump() is called to print the first 32 bytes of imap, the
> first 8 members in struct dinomap are the first 32 bytes of imap, because
> in_diskblock and in_maxag are not initialized when imap is created.
> 
> When creating imap, set in_diskblock and in_maxag to 0 to prevent this
> issue from happening.

Thanks for the patch, but I received two patches to fix this today, and 
I am opting for the other one which uses kzalloc to zero the structure.

Shaggy

> 
> [1]
> BUG: KMSAN: uninit-value in hex_dump_to_buffer+0x888/0x1100 lib/hexdump.c:171
>   hex_dump_to_buffer+0x888/0x1100 lib/hexdump.c:171
>   print_hex_dump+0x13d/0x3e0 lib/hexdump.c:276
>   diFree+0x5ba/0x4350 fs/jfs/jfs_imap.c:876
>   jfs_evict_inode+0x510/0x550 fs/jfs/inode.c:156
>   evict+0x723/0xd10 fs/inode.c:796
>   iput_final fs/inode.c:1946 [inline]
>   iput+0x97b/0xdb0 fs/inode.c:1972
>   txUpdateMap+0xf3e/0x1150 fs/jfs/jfs_txnmgr.c:2367
>   txLazyCommit fs/jfs/jfs_txnmgr.c:2664 [inline]
>   jfs_lazycommit+0x627/0x11d0 fs/jfs/jfs_txnmgr.c:2733
>   kthread+0x6b9/0xef0 kernel/kthread.c:464
>   ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:148
>   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 
> Uninit was created at:
>   slab_post_alloc_hook mm/slub.c:4121 [inline]
>   slab_alloc_node mm/slub.c:4164 [inline]
>   __kmalloc_cache_noprof+0x8e3/0xdf0 mm/slub.c:4320
>   kmalloc_noprof include/linux/slab.h:901 [inline]
>   diMount+0x61/0x7f0 fs/jfs/jfs_imap.c:105
>   jfs_mount+0xa8e/0x11d0 fs/jfs/jfs_mount.c:176
>   jfs_fill_super+0xa47/0x17c0 fs/jfs/super.c:523
>   get_tree_bdev_flags+0x6ec/0x910 fs/super.c:1636
>   get_tree_bdev+0x37/0x50 fs/super.c:1659
>   jfs_get_tree+0x34/0x40 fs/jfs/super.c:635
>   vfs_get_tree+0xb1/0x5a0 fs/super.c:1814
>   do_new_mount+0x71f/0x15e0 fs/namespace.c:3560
>   path_mount+0x742/0x1f10 fs/namespace.c:3887
>   do_mount fs/namespace.c:3900 [inline]
>   __do_sys_mount fs/namespace.c:4111 [inline]
>   __se_sys_mount+0x71f/0x800 fs/namespace.c:4088
>   __x64_sys_mount+0xe4/0x150 fs/namespace.c:4088
>   x64_sys_call+0x39bf/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:166
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
> 
> Reported-by: syzbot+df6cdcb35904203d2b6d@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=df6cdcb35904203d2b6d
> Signed-off-by: Edward Adam Davis <eadavis@...com>
> ---
>   fs/jfs/jfs_imap.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/fs/jfs/jfs_imap.c b/fs/jfs/jfs_imap.c
> index a360b24ed320..ff32b614a09b 100644
> --- a/fs/jfs/jfs_imap.c
> +++ b/fs/jfs/jfs_imap.c
> @@ -134,6 +134,8 @@ int diMount(struct inode *ipimap)
>   		imap->im_agctl[index].numfree =
>   		    le32_to_cpu(dinom_le->in_agctl[index].numfree);
>   	}
> +	imap->im_diskblock = 0;
> +	imap->im_maxag = 0;
>   
>   	/* release the buffer. */
>   	release_metapage(mp);