APPLIED [OEM-5.6] Re: [SRU Focal, Focal/oem-5.6] xfs: fix boundary test in xfs_attr_shortform_verify

[Timo Aaltonen]

On 16.9.2020 20.50, Thadeu Lima de Souza Cascardo wrote:
> From: Eric Sandeen <sandeen at redhat.com>
> 
> The boundary test for the fixed-offset parts of xfs_attr_sf_entry in
> xfs_attr_shortform_verify is off by one, because the variable array
> at the end is defined as nameval[1] not nameval[].
> Hence we need to subtract 1 from the calculation.
> 
> This can be shown by:
> 
> and verifications will fail when it's written to disk.
> 
> This only matters for a last attribute which has a single-byte name
> and no value, otherwise the combination of namelen & valuelen will
> push endp further out and this test won't fail.
> 
> Fixes: 1e1bbd8e7ee06 ("xfs: create structure verifier function for shortform xattrs")
> Signed-off-by: Eric Sandeen <sandeen at redhat.com>
> Reviewed-by: Darrick J. Wong <darrick.wong at oracle.com>
> Signed-off-by: Darrick J. Wong <darrick.wong at oracle.com>
> Reviewed-by: Christoph Hellwig <hch at lst.de>
> (cherry picked from commit f4020438fab05364018c91f7e02ebdd192085933)
> CVE-2020-14385
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
> ---
>  fs/xfs/libxfs/xfs_attr_leaf.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
> index fed537a4353d..54c412549edf 100644
> --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> @@ -1010,8 +1010,10 @@ xfs_attr_shortform_verify(
>  		 * struct xfs_attr_sf_entry has a variable length.
>  		 * Check the fixed-offset parts of the structure are
>  		 * within the data buffer.
> +		 * xfs_attr_sf_entry is defined with a 1-byte variable
> +		 * array at the end, so we must subtract that off.
>  		 */
> -		if (((char *)sfep + sizeof(*sfep)) >= endp)
> +		if (((char *)sfep + sizeof(*sfep) - 1) >= endp)
>  			return __this_address;
>  
>  		/* Don't allow names with known bad length. */
> 

applied to oem-5.6, thanks

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