xfs: fix a UAF problem in xattr repair

The xchk_setup_xattr_buf function can allocate a new value buffer, which
means that any reference to ab->value before the call could become a
dangling pointer.  Fix this by moving an assignment to after the buffer
setup.

Cc: stable@vger.kernel.org # v6.10
Fixes: e47dcf1 ("xfs: repair extended attributes")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

Author: Darrick J. Wong

fs/xfs/scrub/attr_repair.c

@@ -333,7 +333,6 @@ xrep_xattr_salvage_remote_attr(
 		.attr_filter		= ent->flags & XFS_ATTR_NSP_ONDISK_MASK,
 		.namelen		= rentry->namelen,
 		.name			= rentry->name,
-		.value			= ab->value,
 		.valuelen		= be32_to_cpu(rentry->valuelen),
 	};
 	unsigned int			namesize;
@@ -363,6 +362,7 @@ xrep_xattr_salvage_remote_attr(
 		error = -EDEADLOCK;
 	if (error)
 		return error;
+	args.value = ab->value;
 
 	/* Look up the remote value and stash it for reconstruction. */
 	error = xfs_attr3_leaf_getvalue(leaf_bp, &args);