linux-kernel - Re: [PATCH] ext4: xattr: fix null pointer deref in ext4_raw

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Message-ID: <0fa6cee3-c25e-4649-8f85-8645cacab00e@huawei.com>
Date: Sat, 8 Nov 2025 11:12:44 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Karina Yankevich <k.yankevich@....ru>
CC: Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>,
	Bhupesh <bhupesh@...lia.com>, <linux-ext4@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <lvc-patches@...uxtesting.org>, Sergey
 Shtylyov <s.shtylyov@....ru>
Subject: Re: [PATCH] ext4: xattr: fix null pointer deref in ext4_raw_inode()

On 2025-10-22 17:32, Karina Yankevich wrote:
> If ext4_get_inode_loc() fails (e.g. if it returns -EFSCORRUPTED),
> iloc.bh will remain set to NULL. Since ext4_xattr_inode_dec_ref_all()
> lacks error checking, this will lead to a null pointer dereference
> in ext4_raw_inode(), called right after ext4_get_inode_loc().
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Fixes: c8e008b60492 ("ext4: ignore xattrs past end")
> Signed-off-by: Karina Yankevich <k.yankevich@....ru>
> Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>

An error return at this point may lead to an inconsistent ea_inode
reference count. However, since the caller ext4_xattr_delete_inode()
has already loaded iloc.bh via ext4_get_inode_loc(), this almost never
fails.

Reviewed-by: Baokun Li <libaokun1@...wei.com>

> ---
>  fs/ext4/xattr.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index ce7253b3f549..2e02efbddaac 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -1174,7 +1174,11 @@ ext4_xattr_inode_dec_ref_all(handle_t *handle, struct inode *parent,
>  	if (block_csum)
>  		end = (void *)bh->b_data + bh->b_size;
>  	else {
> -		ext4_get_inode_loc(parent, &iloc);
> +		err = ext4_get_inode_loc(parent, &iloc);
> +		if (err) {
> +			EXT4_ERROR_INODE(parent, "parent inode loc (error %d)", err);
> +			return;
> +		}
>  		end = (void *)ext4_raw_inode(&iloc) + EXT4_SB(parent->i_sb)->s_inode_size;
>  	}
>