linux-kernel - Re: [PATCH v2] udf: avoid uninitialized variable use

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Date:	Mon, 4 Jan 2016 10:56:05 +0100
From:	Jan Kara <jack@...e.cz>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org, Jan Kara <jack@...e.cz>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] udf: avoid uninitialized variable use

On Fri 01-01-16 15:21:54, Arnd Bergmann wrote:
> A new warning about a real bug has come up from a recent cleanup:
> 
> fs/udf/inode.c: In function 'udf_setup_indirect_aext':
> fs/udf/inode.c:1927:28: warning: 'adsize' may be used uninitialized in this function [-Wmaybe-uninitialized]
> 
> If the alloc_type is neither ICBTAG_FLAG_AD_SHORT nor ICBTAG_FLAG_AD_LONG,
> the value of adsize is undefined. This changes the code to use zero for adsize
> in that case, which may be the correct solution, though I have not looked
> at the code in enough detail to know if it should be something else instead.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Fixes: fcea62babc81 ("udf: Factor out code for creating indirect extent")
> ---
> sorry for missing another instance the first time around. The warning is
> a bit unreliable and it seems in my first configuration I got it only
> for one of the two instances that show it in other configuration.
> 
> After checking the remaining functions in this file for the same possible
> problem, I found that the other functions use either 'BUG()' or 'return -EIO'
> in the 'else' path, so I assume the two functions here should one of those
> as well, but I don't know which.

Callers of these functions make sure alloc_type is one of the two valid
ones. However for future-proofing you're right that probably we should
handle the invalid case as well. Setting adsize to zero is problematic -
not sure what the code would actually do but it wouldn't definitely work.
I'd just return -EIO. Attached is the patch I have merged.

								Honza
> 
> diff --git a/fs/udf/inode.c b/fs/udf/inode.c
> index 5b83351041a4..42f68dd7e6ef 100644
> --- a/fs/udf/inode.c
> +++ b/fs/udf/inode.c
> @@ -1890,6 +1890,8 @@ int udf_setup_indirect_aext(struct inode *inode, int block,
>  		adsize = sizeof(struct short_ad);
>  	else if (UDF_I(inode)->i_alloc_type == ICBTAG_FLAG_AD_LONG)
>  		adsize = sizeof(struct long_ad);
> +	else
> +		adsize = 0;
>  
>  	neloc.logicalBlockNum = block;
>  	neloc.partitionReferenceNum = epos->block.partitionReferenceNum;
> @@ -1963,6 +1965,8 @@ int __udf_add_aext(struct inode *inode, struct extent_position *epos,
>  		adsize = sizeof(struct short_ad);
>  	else if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_LONG)
>  		adsize = sizeof(struct long_ad);
> +	else
> +		adsize = 0;
>  
>  	if (!epos->bh) {
>  		WARN_ON(iinfo->i_lenAlloc !=
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

View attachment "0001-udf-avoid-uninitialized-variable-use.patch" of type "text/x-patch" (1747 bytes)